feat: add wacc-compiler to the project

Merge request lab2425_spring/WACC_37!46

.commitlintrc.js

@@ -0,0 +1,4 @@
+export default {
+  extends: ['@commitlint/config-conventional'],
+  ignores: [commit => commit.startsWith("Local Mutable Chains\n")]
+}

.commitlintrc.yml

@@ -1 +0,0 @@
-extends: "@commitlint/config-conventional"

.gitignore

@@ -3,3 +3,4 @@
 .scala-build/
 .vscode/
 wacc-examples/
+.idea/

.gitlab-ci.yml

@@ -30,9 +30,10 @@ check_commits:
   before_script:
     - apk add git
     - npm install -g @commitlint/cli @commitlint/config-conventional
-    - git pull origin master
+    - git checkout origin/master
   script:
-    - npx commitlint --from origin/master --to HEAD --verbose
+    - git checkout ${CI_COMMIT_SHA}
+    - npx commitlint --from origin/master --to ${CI_COMMIT_SHA} --verbose
 
 compile_jvm:
   stage: compile
@@ -45,12 +46,13 @@ compile_jvm:
       - .scala-build/
 
 test_jvm:
+  image: gumjoe/wacc-ci-scala:x86
   stage: test
   # Use our own runner (not cloud VM or shared) to ensure we have multiple cores.
-  tags: [ large ]
+  tags: [large]
   # This is expensive, so do use `dependencies` instead of `needs` to
   # ensure all previous stages pass.
-  dependencies: [ compile_jvm ]
+  dependencies: [compile_jvm]
   before_script:
     - git clone https://$EXAMPLES_AUTH@gitlab.doc.ic.ac.uk/lab2425_spring/wacc-examples.git
   script:

compile

@@ -4,6 +4,6 @@
 # but do *not* change its name.
 
 # feel free to adjust to suit the specific internal flags of your compiler
-./wacc-compiler "$@"
+./wacc-compiler --output . "$@"
 
 exit $?

extension/examples/invalid/semantics/badWacc.wacc

@@ -0,0 +1,10 @@
+begin
+  int main() is
+    int a = 5 ;
+    string b = "Hello" ;
+    return a + b
+  end
+
+  int result = call main() ;
+  exit result
+end

extension/examples/invalid/semantics/imports/importBadFile.wacc

@@ -0,0 +1,6 @@
+import "./doesNotExist.wacc" (main)
+
+begin
+  int result = call main() ;
+  exit result
+end

extension/examples/invalid/semantics/imports/importBadFunc.wacc

@@ -0,0 +1,6 @@
+import "../../../valid/sum.wacc" (mult)
+
+begin
+  int result = call mult(3, 2) ;
+  exit result
+end

extension/examples/invalid/semantics/imports/importBadSem.wacc

@@ -0,0 +1,10 @@
+import "../badWacc.wacc" (main)
+
+begin
+  int sum(int a, int b) is
+    return a + b
+  end
+
+  int result = call main() ;
+  exit result
+end

extension/examples/invalid/semantics/imports/importBadSem2.wacc

@@ -0,0 +1,6 @@
+import "./importBadSem.wacc" (sum)
+
+begin
+  int result = call sum(1, 2) ;
+  exit result
+end

extension/examples/invalid/semantics/imports/inderect.wacc

@@ -0,0 +1,6 @@
+import "../../../valid/imports/basic.wacc" (sum)
+
+begin
+  int result = call sum(3, 2) ;
+  exit result
+end

extension/examples/invalid/syntax/badWacc.wacc

@@ -0,0 +1,6 @@
+int main() is
+  println "Hello World!" ;
+  return 0
+end
+
+skip

extension/examples/invalid/syntax/imports/emptyImport.wacc

@@ -0,0 +1,8 @@
+import "../../../valid/sum.wacc" sum, main
+
+begin
+  int result1 = call sum(5, 10) ;
+  int result2 = call main() ;
+  println result1 ;
+  println result2
+end

extension/examples/invalid/syntax/imports/emptyImport2.wacc

@@ -0,0 +1,5 @@
+import "../../../valid/sum.wacc" ()
+
+begin
+  exit 0
+end

extension/examples/invalid/syntax/imports/importBadSyntax.wacc

@@ -0,0 +1,10 @@
+import "../badWacc.wacc" (main)
+
+begin
+  int sum(int a, int b) is
+    return a + b
+  end
+
+  int result = call main() ;
+  exit result
+end

extension/examples/invalid/syntax/imports/importBadSyntax2.wacc

@@ -0,0 +1,6 @@
+import "./importBadSyntax.wacc" (sum)
+
+begin
+  int result = call sum(1, 2) ;
+  exit result
+end

extension/examples/invalid/syntax/imports/importNoParens.wacc

@@ -0,0 +1 @@
+

extension/examples/invalid/syntax/imports/importSemis.wacc

@@ -0,0 +1,9 @@
+import "../../../valid/sum.wacc" (sum) ;
+import "../../../valid/sum.wacc" (main) ;
+
+begin
+  int result1 = call sum(5, 10) ;
+  int result2 = call main() ;
+  println result1 ;
+  println result2
+end

extension/examples/invalid/syntax/imports/importStar.wacc

@@ -0,0 +1,5 @@
+import "../../../valid/sum.wacc" *
+
+begin
+  exit 0
+end

extension/examples/invalid/syntax/imports/importStar2.wacc

@@ -0,0 +1,5 @@
+import "../../../valid/sum.wacc" (*)
+
+begin
+  exit 0
+end

extension/examples/valid/.gitignore

@@ -0,0 +1,7 @@
+*
+
+!imports/
+imports/*
+
+!.gitignore
+!*.wacc

extension/examples/valid/imports/alias.wacc

@@ -0,0 +1,22 @@
+# import main from ../sum.wacc and ./basic.wacc
+
+# Output:
+# 15
+# 0
+# -33
+#
+
+# Exit:
+# 0
+
+# Program:
+
+import "../sum.wacc" (main as sumMain)
+import "./basic.wacc" (main)
+
+begin
+  int result1 = call sumMain() ;
+  int result2 = call main() ;
+  println result1 ;
+  println result2
+end

extension/examples/valid/imports/basic.wacc

@@ -0,0 +1,21 @@
+# import sum from ../sum.wacc
+
+# Output:
+# -33
+#
+
+# Exit:
+# 0
+
+# Program:
+
+import "../sum.wacc" (sum)
+
+begin
+  int main() is 
+    int result = call sum(-10, -23) ;
+    return result
+  end
+  int result = call main() ;
+  println result
+end

extension/examples/valid/imports/manyMains.wacc

@@ -0,0 +1,33 @@
+# import all the mains
+
+# Output:
+# 15
+# -33
+# 0
+# -33
+# 0
+#
+
+# Exit:
+# 99
+
+# Program:
+
+import "../sum.wacc" (main as sumMain)
+import "./basic.wacc" (main as basicMain)
+import "./multiFunc.wacc" (main as multiFuncMain)
+
+begin
+  int main() is 
+    int result1 = call sumMain() ;
+    int result2 = call basicMain() ;
+    int result3 = call multiFuncMain() ;
+    println result1 ;
+    println result2 ;
+    println result3 ;
+    return 99
+  end
+
+  int result = call main() ;
+  exit result
+end

extension/examples/valid/imports/multiFunc.wacc

@@ -0,0 +1,27 @@
+# import sum, main from ../sum.wacc
+
+# Output:
+# 15
+# -33
+# 0
+# 0
+#
+
+# Exit:
+# 0
+
+# Program:
+
+import "../sum.wacc" (sum, main as sumMain)
+
+begin
+  int main() is 
+    int result = call sum(-10, -23) ;
+    println result ;
+    return 0
+  end
+  int result1 = call sumMain() ;
+  int result2 = call main() ;
+  println result1 ;
+  println result2
+end

extension/examples/valid/sum.wacc

@@ -0,0 +1,27 @@
+# simple sum program
+
+# Output:
+# 15
+#
+
+# Exit:
+# 0
+
+# Program:
+
+begin
+  int sum(int a, int b) is 
+    return a + b
+  end
+
+  int main() is
+    int a = 5 ;
+    int b = 10 ;
+    int result = call sum(a, b) ;
+    println result ;
+    return 0
+  end
+
+  int result = call main() ;
+  exit result
+end

project.scala

@@ -3,25 +3,22 @@
 
 // dependencies
 //> using dep com.github.j-mie6::parsley::5.0.0-M10
-//> using dep com.github.j-mie6::parsley-cats::1.3.0
-//> using dep com.lihaoyi::os-lib::0.11.3
-//> using dep com.github.scopt::scopt::4.1.0
+//> using dep com.github.j-mie6::parsley-cats::1.5.0
+//> using dep com.lihaoyi::os-lib::0.11.4
+//> using dep org.typelevel::cats-core::2.13.0
+//> using dep org.typelevel::cats-effect::3.5.7
+//> using dep com.monovore::decline::2.5.0
+//> using dep com.monovore::decline-effect::2.5.0
+//> using dep org.typelevel::log4cats-slf4j::2.7.0
+//> using dep org.slf4j:slf4j-simple:2.0.17
 //> using test.dep org.scalatest::scalatest::3.2.19
+//> using dep org.typelevel::cats-effect-testing-scalatest::1.6.0
+//> using dep "co.fs2::fs2-core:3.11.0"
+//> using dep co.fs2::fs2-io:3.11.0
 
-// these are all sensible defaults to catch annoying issues
+// sensible defaults for warnings and compiler checks
 //> using options -deprecation -unchecked -feature
 //> using options -Wimplausible-patterns -Wunused:all
 //> using options -Yexplicit-nulls -Wsafe-init -Xkind-projector:underscores
 
-// these will help ensure you have access to the latest parsley releases
-// even before they land on maven proper, or snapshot versions, if necessary.
-// just in case they cause problems, however, keep them turned off unless you
-// specifically need them.
-// using repositories sonatype-s01:releases
-// using repositories sonatype-s01:snapshots
-
-// these are flags used by Scala native: if you aren't using scala-native, then they do nothing
-// lto-thin has decent linking times, and release-fast does not too much optimisation.
-// using nativeLto thin
-// using nativeGc commix
-// using nativeMode release-fast
+// repositories for pre-release versions if needed

src/main/wacc/Error.scala

@@ -1,93 +0,0 @@
-package wacc
-
-import wacc.ast.Position
-import wacc.types._
-
-/** Error types for semantic errors
-  */
-enum Error {
-  case DuplicateDeclaration(ident: ast.Ident)
-  case UndeclaredVariable(ident: ast.Ident)
-  case UndefinedFunction(ident: ast.Ident)
-
-  case FunctionParamsMismatch(ident: ast.Ident, expected: Int, got: Int, funcType: FuncType)
-  case SemanticError(pos: Position, msg: String)
-  case TypeMismatch(pos: Position, expected: SemType, got: SemType, msg: String)
-  case InternalError(pos: Position, msg: String)
-}
-
-/** Function to handle printing the details of a given semantic error
-  *
-  * @param error
-  *   Error object
-  * @param errorContent
-  *   Contents of the file to generate code snippets
-  */
-def printError(error: Error)(using errorContent: String): Unit = {
-  println("Semantic error:")
-  error match {
-    case Error.DuplicateDeclaration(ident) =>
-      printPosition(ident.pos)
-      println(s"Duplicate declaration of identifier ${ident.v}")
-      highlight(ident.pos, ident.v.length)
-    case Error.UndeclaredVariable(ident) =>
-      printPosition(ident.pos)
-      println(s"Undeclared variable ${ident.v}")
-      highlight(ident.pos, ident.v.length)
-    case Error.UndefinedFunction(ident) =>
-      printPosition(ident.pos)
-      println(s"Undefined function ${ident.v}")
-      highlight(ident.pos, ident.v.length)
-    case Error.FunctionParamsMismatch(id, expected, got, funcType) =>
-      printPosition(id.pos)
-      println(s"Function expects $expected parameters, got $got")
-      println(
-        s"(function ${id.v} has type (${funcType.params.mkString(", ")}) -> ${funcType.returnType})"
-      )
-      highlight(id.pos, 1)
-    case Error.TypeMismatch(pos, expected, got, msg) =>
-      printPosition(pos)
-      println(s"Type mismatch: $msg\nExpected: $expected\nGot: $got")
-      highlight(pos, 1)
-    case Error.SemanticError(pos, msg) =>
-      printPosition(pos)
-      println(msg)
-      highlight(pos, 1)
-    case wacc.Error.InternalError(pos, msg) =>
-      printPosition(pos)
-      println(s"Internal error: $msg")
-      highlight(pos, 1)
-  }
-
-}
-
-/** Function to highlight a section of code for an error message
-  *
-  * @param pos
-  *   Position of the error
-  * @param size
-  *   Size(in chars) of section to highlight
-  * @param errorContent
-  *   Contents of the file to generate code snippets
-  */
-def highlight(pos: Position, size: Int)(using errorContent: String): Unit = {
-  val lines = errorContent.split("\n")
-
-  val preLine = if (pos.line > 1) lines(pos.line - 2) else ""
-  val midLine = lines(pos.line - 1)
-  val postLine = if (pos.line < lines.size) lines(pos.line) else ""
-  val linePointer = " " * (pos.column + 2) + ("^" * (size)) + "\n"
-
-  println(
-    s"  >$preLine\n  >$midLine\n$linePointer  >$postLine"
-  )
-}
-
-/** Function to print the position of an error
-  *
-  * @param pos
-  *   Position of the error
-  */
-def printPosition(pos: Position): Unit = {
-  println(s"(line ${pos.line}, column ${pos.column}):")
-}

src/main/wacc/Main.scala

@@ -1,56 +1,177 @@
 package wacc
 
-import scala.collection.mutable
+import cats.data.{Chain, NonEmptyList}
 import parsley.{Failure, Success}
-import scopt.OParser
+
+import java.nio.file.{Files, Path}
+import cats.syntax.all._
+
+import cats.effect.IO
+import cats.effect.ExitCode
+
+import com.monovore.decline._
+import com.monovore.decline.effect._
+
+import org.typelevel.log4cats.slf4j.Slf4jLogger
+import org.typelevel.log4cats.Logger
+
+import fs2.Stream
+
+import assemblyIR as asm
+import cats.data.ValidatedNel
 import java.io.File
+import cats.data.NonEmptySeq
 
-case class CliConfig(
-    file: File = new File(".")
-)
+/*
+TODO:
+  1) IO correctness
+  2) Errors can be handled more gracefully - currently, parallelised compilation is not fail fast as far as I am aware
+  3) splitting the file up and nicer refactoring
+  4) logging could be removed
+  5) general cleanup and comments (things like replacing home/<user> with ~ , and names of parameters and args, descriptions etc)
+ */
 
-val cliBuilder = OParser.builder[CliConfig]
-val cliParser = {
-  import cliBuilder._
-  OParser.sequence(
-    programName("wacc-compiler"),
-    help('h', "help")
-      .text("Prints this help message"),
-    arg[File]("<file>")
-      .text("Input WACC source file")
-      .required()
-      .action((f, c) => c.copy(file = f))
-      .validate(f =>
-        if (!f.exists) failure("File does not exist")
-        else if (!f.isFile) failure("File must be a regular file")
-        else if (!f.getName.endsWith(".wacc"))
-          failure("File must have .wacc extension")
-        else success
-      )
-  )
+private val SUCCESS = ExitCode.Success.code
+private val ERROR = ExitCode.Error.code
+
+given logger: Logger[IO] = Slf4jLogger.getLogger[IO]
+
+val logOpt: Opts[Boolean] =
+  Opts.flag("log", "Enable logging for additional compilation details", short = "l").orFalse
+
+def validateFile(path: Path): ValidatedNel[String, Path] = {
+  (for {
+    // TODO: redundant 2nd parameter :(
+    _ <- Either.cond(Files.exists(path), (), s"File '${path}' does not exist")
+    _ <- Either.cond(Files.isRegularFile(path), (), s"File '${path}' must be a regular file")
+    _ <- Either.cond(path.toString.endsWith(".wacc"), (), "File must have .wacc extension")
+  } yield path).toValidatedNel
 }
 
-def compile(contents: String): Int = {
+val filesOpt: Opts[NonEmptyList[Path]] =
+  Opts.arguments[Path]("files").mapValidated {
+    _.traverse(validateFile)
+  }
+
+val outputOpt: Opts[Option[Path]] =
+  Opts
+    .option[Path]("output", metavar = "path", help = "Output directory for compiled files.")
+    .validate("Must have permissions to create & access the output path") { path =>
+      try {
+        Files.createDirectories(path)
+        true
+      } catch {
+        case e: java.nio.file.AccessDeniedException =>
+          false
+      }
+    }
+    .validate("Output path must be a directory") { path =>
+      Files.isDirectory(path)
+    }
+    .orNone
+
+def frontend(
+    contents: String,
+    file: File
+): IO[Either[NonEmptySeq[Error], microWacc.Program]] =
   parser.parse(contents) match {
-    case Success(prog) =>
-      given errors: mutable.Builder[Error, List[Error]] = List.newBuilder
-      val (names, funcs) = renamer.rename(prog)
-      given ctx: typeChecker.TypeCheckerCtx = typeChecker.TypeCheckerCtx(names, funcs, errors)
-      typeChecker.check(prog)
-      if (errors.result.nonEmpty) {
-        given errorContent: String = contents
-        errors.result.foreach(printError)
-        200
-      } else 0
-    case Failure(msg) =>
-      println(msg)
-      100
+    case Failure(msg) => IO.pure(Left(NonEmptySeq.one(Error.SyntaxError(file, msg))))
+    case Success(fn) =>
+      val partialProg = fn(file)
+
+      for {
+        (typedProg, errors) <- semantics.check(partialProg)
+        res = NonEmptySeq.fromSeq(errors.iterator.toSeq).map(Left(_)).getOrElse(Right(typedProg))
+      } yield res
   }
+
+def backend(typedProg: microWacc.Program): Chain[asm.AsmLine] =
+  asmGenerator.generateAsm(typedProg)
+
+def compile(
+    filePath: Path,
+    outputDir: Option[Path],
+    log: Boolean
+): IO[Int] = {
+  val logAction: String => IO[Unit] =
+    if (log) logger.info(_)
+    else (_ => IO.unit)
+
+  def readSourceFile: IO[String] =
+    IO.blocking(os.read(os.Path(filePath)))
+
+  // TODO: path, file , the names are confusing (when Path is the type but we are working with files)
+  def writeOutputFile(typedProg: microWacc.Program, outputPath: Path): IO[Unit] =
+    val backendStart = System.nanoTime()
+    val asmLines = backend(typedProg)
+    val backendEnd = System.nanoTime()
+    writer.writeTo(asmLines, outputPath) *>
+      logAction(
+        s"Backend time (${filePath.toRealPath()}): ${(backendEnd - backendStart).toFloat / 1e6} ms"
+      ) *>
+      IO.blocking(println(s"Success: ${outputPath.toRealPath()}"))
+
+  def processProgram(contents: String, file: File, outDir: Path): IO[Int] =
+    val frontendStart = System.nanoTime()
+    for {
+      frontendResult <- frontend(contents, file)
+      frontendEnd = System.nanoTime()
+      _ <- logAction(
+        s"Frontend time (${filePath.toRealPath()}): ${(frontendEnd - frontendStart).toFloat / 1e6} ms"
+      )
+      res <- frontendResult match {
+        case Left(errors) =>
+          val code = errors.map(err => err.exitCode).toList.min
+          val errorMsg = errors.map(formatError).toIterable.mkString("\n")
+          for {
+            _ <- logAction(s"Compilation failed for $filePath\nExit code: $code")
+            _ <- IO.blocking(
+              // Explicit println since we want this to always show without logger thread info e.t.c.
+              println(s"Compilation failed for ${file.getCanonicalPath}:\n$errorMsg")
+            )
+          } yield code
+
+        case Right(typedProg) =>
+          val outputFile = outDir.resolve(filePath.getFileName.toString.stripSuffix(".wacc") + ".s")
+          writeOutputFile(typedProg, outputFile).as(SUCCESS)
+      }
+    } yield res
+
+  for {
+    contents <- readSourceFile
+    _ <- logAction(s"Compiling file: ${filePath.toAbsolutePath}")
+    exitCode <- processProgram(contents, filePath.toFile, outputDir.getOrElse(filePath.getParent))
+  } yield exitCode
 }
 
-def main(args: Array[String]): Unit =
-  OParser.parse(cliParser, args, CliConfig()) match {
-    case Some(config) =>
-      System.exit(compile(os.read(os.Path(config.file.getAbsolutePath))))
-    case None =>
-  }
+def compileCommandParallel(
+    files: NonEmptyList[Path],
+    log: Boolean,
+    outDir: Option[Path]
+): IO[ExitCode] =
+  Stream
+    .emits(files.toList)
+    .parEvalMapUnordered(Runtime.getRuntime.availableProcessors()) { file =>
+      compile(file.toAbsolutePath, outDir, log)
+    }
+    .compile
+    .toList
+    .map { exitCodes =>
+      exitCodes.filter(_ != 0) match {
+        case Nil        => ExitCode.Success
+        case errorCodes => ExitCode(errorCodes.min)
+      }
+    }
+
+object Main
+    extends CommandIOApp(
+      name = "wacc",
+      header = "The ultimate WACC compiler",
+      version = "1.0"
+    ) {
+  def main: Opts[IO[ExitCode]] =
+    (filesOpt, logOpt, outputOpt).mapN { (files, log, outDir) =>
+      compileCommandParallel(files, log, outDir)
+    }
+
+}

src/main/wacc/backend/LabelGenerator.scala

@@ -0,0 +1,78 @@
+package wacc
+
+import scala.collection.mutable
+import cats.data.Chain
+import wacc.ast.Position
+
+private class LabelGenerator {
+  import assemblyIR._
+  import microWacc.{CallTarget, Ident, Builtin}
+  import asmGenerator.escaped
+
+  private val strings = mutable.HashMap[String, String]()
+  private val files = mutable.HashMap[String, Int]()
+  private var labelVal = -1
+  private var permittedFuncFile: Option[String] = None
+
+  /** Get an arbitrary label. */
+  def getLabel(): String = {
+    labelVal += 1
+    s".L$labelVal"
+  }
+
+  private def getLabel(target: CallTarget | RuntimeError): String = target match {
+    case Ident(v, guid)    => s"wacc_${v}_$guid"
+    case Builtin(name)     => s"_$name"
+    case err: RuntimeError => s".L.${err.name}"
+  }
+
+  /** Get a named label def for a function or error. */
+  def getLabelDef(target: CallTarget | RuntimeError): LabelDef =
+    LabelDef(getLabel(target))
+
+  /** Get a named label for a function or error. */
+  def getLabelArg(target: CallTarget | RuntimeError): LabelArg =
+    LabelArg(getLabel(target))
+
+  /** Get an arbitrary label for a string. */
+  def getLabelArg(str: String): LabelArg =
+    LabelArg(strings.getOrElseUpdate(str, s".L.str${strings.size}"))
+
+  /** Get a named label for a string. */
+  def getLabelArg(src: String, name: String): LabelArg =
+    LabelArg(strings.getOrElseUpdate(src, s".L.$name.str${strings.size}"))
+
+  /** Get a debug directive for a file. */
+  def getDebugFile(file: java.io.File): Int =
+    files.getOrElseUpdate(file.getCanonicalPath, files.size)
+
+  /** Get a debug directive for a function. */
+  def getDebugFunc(pos: Position, name: String, label: LabelDef): Chain[AsmLine] = {
+    permittedFuncFile match {
+      case Some(f) if f != pos.file.getCanonicalPath => Chain.empty
+      case _ =>
+        val customLabel = if name == "main" then Chain.empty else Chain(LabelDef(name))
+        permittedFuncFile = Some(pos.file.getCanonicalPath)
+        customLabel ++ Chain(
+          Directive.Location(getDebugFile(pos.file), pos.line, None),
+          Directive.Type(label, SymbolType.Function),
+          Directive.Func(name, label)
+        )
+    }
+  }
+
+  /** Generate the assembly labels for constants that were labelled using the LabelGenerator. */
+  def generateConstants: Chain[AsmLine] =
+    strings.foldLeft(Chain.empty) { case (acc, (str, label)) =>
+      acc ++ Chain(
+        LabelDef(label),
+        Directive.Asciz(str.escaped)
+      )
+    }
+
+  /** Generates debug directives that were created using the LabelGenerator. */
+  def generateDebug: Chain[AsmLine] =
+    files.foldLeft(Chain.empty) { case (acc, (file, no)) =>
+      acc :+ Directive.File(no, file)
+    }
+}

src/main/wacc/backend/RuntimeError.scala

@@ -0,0 +1,112 @@
+package wacc
+
+import cats.data.Chain
+import wacc.assemblyIR._
+
+sealed trait RuntimeError {
+  val name: String
+  protected val errStr: String
+
+  protected def getErrLabel(using labelGenerator: LabelGenerator): LabelArg =
+    labelGenerator.getLabelArg(errStr, name = name)
+
+  protected def generateHandler(using labelGenerator: LabelGenerator): Chain[AsmLine]
+
+  def generate(using labelGenerator: LabelGenerator): Chain[AsmLine] =
+    labelGenerator.getLabelDef(this) +: generateHandler
+}
+
+object RuntimeError {
+  import wacc.asmGenerator.stackAlign
+  import assemblyIR.commonRegisters._
+
+  private val ERROR_CODE = 255
+
+  case object ZeroDivError extends RuntimeError {
+    val name = "errDivZero"
+    protected val errStr = "fatal error: division or modulo by zero"
+
+    protected def generateHandler(using labelGenerator: LabelGenerator): Chain[AsmLine] = Chain(
+      stackAlign,
+      Load(RDI, MemLocation(RIP, getErrLabel)),
+      assemblyIR.Call(CLibFunc.PrintF),
+      Move(RDI, ImmediateVal(-1)),
+      assemblyIR.Call(CLibFunc.Exit)
+    )
+
+  }
+
+  case object BadChrError extends RuntimeError {
+    val name = "errBadChr"
+    protected val errStr = "fatal error: int %d is not an ASCII character 0-127"
+
+    protected def generateHandler(using labelGenerator: LabelGenerator): Chain[AsmLine] = Chain(
+      Pop(RSI),
+      stackAlign,
+      Load(RDI, MemLocation(RIP, getErrLabel)),
+      assemblyIR.Call(CLibFunc.PrintF),
+      Move(RDI, ImmediateVal(ERROR_CODE)),
+      assemblyIR.Call(CLibFunc.Exit)
+    )
+
+  }
+
+  case object NullPtrError extends RuntimeError {
+    val name = "errNullPtr"
+    protected val errStr = "fatal error: null pair dereferenced or freed"
+
+    protected def generateHandler(using labelGenerator: LabelGenerator): Chain[AsmLine] = Chain(
+      stackAlign,
+      Load(RDI, MemLocation(RIP, getErrLabel)),
+      assemblyIR.Call(CLibFunc.PrintF),
+      Move(RDI, ImmediateVal(ERROR_CODE)),
+      assemblyIR.Call(CLibFunc.Exit)
+    )
+
+  }
+
+  case object OverflowError extends RuntimeError {
+    val name = "errOverflow"
+    protected val errStr = "fatal error: integer overflow or underflow occurred"
+
+    protected def generateHandler(using labelGenerator: LabelGenerator): Chain[AsmLine] = Chain(
+      stackAlign,
+      Load(RDI, MemLocation(RIP, getErrLabel)),
+      assemblyIR.Call(CLibFunc.PrintF),
+      Move(RDI, ImmediateVal(ERROR_CODE)),
+      assemblyIR.Call(CLibFunc.Exit)
+    )
+
+  }
+
+  case object OutOfBoundsError extends RuntimeError {
+    val name = "errOutOfBounds"
+    protected val errStr = "fatal error: array index %d out of bounds"
+
+    protected def generateHandler(using labelGenerator: LabelGenerator): Chain[AsmLine] = Chain(
+      Move(RSI, RCX),
+      stackAlign,
+      Load(RDI, MemLocation(RIP, getErrLabel)),
+      assemblyIR.Call(CLibFunc.PrintF),
+      Move(RDI, ImmediateVal(ERROR_CODE)),
+      assemblyIR.Call(CLibFunc.Exit)
+    )
+  }
+
+  case object OutOfMemoryError extends RuntimeError {
+    val name = "errOutOfMemory"
+    protected val errStr = "fatal error: out of memory"
+
+    def generateHandler(using labelGenerator: LabelGenerator): Chain[AsmLine] = Chain(
+      stackAlign,
+      Load(RDI, MemLocation(RIP, getErrLabel)),
+      assemblyIR.Call(CLibFunc.PrintF),
+      Move(RDI, ImmediateVal(ERROR_CODE)),
+      assemblyIR.Call(CLibFunc.Exit)
+    )
+  }
+
+  val all: Chain[RuntimeError] =
+    Chain(ZeroDivError, BadChrError, NullPtrError, OverflowError, OutOfBoundsError,
+      OutOfMemoryError)
+}

src/main/wacc/backend/Stack.scala

@@ -0,0 +1,90 @@
+package wacc
+
+import scala.collection.mutable.LinkedHashMap
+import cats.data.Chain
+
+class Stack {
+  import assemblyIR._
+  import assemblyIR.Size._
+  import sizeExtensions.size
+  import microWacc as mw
+
+  private val RSP = Register(Q64, RegName.SP)
+  private class StackValue(val size: Size, val offset: Int) {
+    def bottom: Int = offset + elemBytes
+  }
+  private val stack = LinkedHashMap[mw.Expr | Int, StackValue]()
+
+  private val elemBytes: Int = Q64.toInt
+  private def sizeBytes: Int = stack.size * elemBytes
+
+  /** The stack's size in bytes. */
+  def size: Int = stack.size
+
+  /** Push an expression onto the stack. */
+  def push(expr: mw.Expr, src: Register): AsmLine = {
+    stack += expr -> StackValue(expr.ty.size, sizeBytes)
+    Push(src)
+  }
+
+  /** Push a value onto the stack. */
+  def push(itemSize: Size, addr: Src): AsmLine = {
+    stack += stack.size -> StackValue(itemSize, sizeBytes)
+    Push(addr)
+  }
+
+  /** Reserve space for a variable on the stack. */
+  def reserve(ident: mw.Ident): AsmLine = {
+    stack += ident -> StackValue(ident.ty.size, sizeBytes)
+    Subtract(RSP, ImmediateVal(elemBytes))
+  }
+
+  /** Reserve space for a register on the stack. */
+  def reserve(src: Register): AsmLine = {
+    stack += stack.size -> StackValue(src.size, sizeBytes)
+    Subtract(RSP, ImmediateVal(src.size.toInt))
+  }
+
+  /** Reserve space for values on the stack.
+    *
+    * @param sizes
+    *   The sizes of the values to reserve space for.
+    */
+  def reserve(sizes: Size*): AsmLine = {
+    sizes.foreach { itemSize =>
+      stack += stack.size -> StackValue(itemSize, sizeBytes)
+    }
+    Subtract(RSP, ImmediateVal(elemBytes * sizes.size))
+  }
+
+  /** Pop a value from the stack into a register. Sizes MUST match. */
+  def pop(dest: Register): AsmLine = {
+    stack.remove(stack.last._1)
+    Pop(dest)
+  }
+
+  /** Drop the top n values from the stack. */
+  def drop(n: Int = 1): AsmLine = {
+    (1 to n).foreach { _ =>
+      stack.remove(stack.last._1)
+    }
+    Add(RSP, ImmediateVal(n * elemBytes))
+  }
+
+  /** Generate AsmLines within a scope, which is reset after the block. */
+  def withScope(block: () => Chain[AsmLine]): Chain[AsmLine] = {
+    val resetToSize = stack.size
+    var lines = block()
+    lines :+= drop(stack.size - resetToSize)
+    lines
+  }
+
+  /** Get an MemLocation for a variable in the stack. */
+  def accessVar(ident: mw.Ident): MemLocation =
+    MemLocation(RSP, sizeBytes - stack(ident).bottom, opSize = Some(stack(ident).size))
+
+  def contains(ident: mw.Ident): Boolean = stack.contains(ident)
+  def head: MemLocation = MemLocation(RSP, opSize = Some(stack.last._2.size))
+
+  override def toString(): String = stack.toString
+}

src/main/wacc/backend/asmGenerator.scala

@@ -0,0 +1,483 @@
+package wacc
+
+import cats.data.Chain
+import cats.syntax.foldable._
+import wacc.RuntimeError._
+
+object asmGenerator {
+  import microWacc._
+  import assemblyIR._
+  import assemblyIR.commonRegisters._
+  import assemblyIR.RegName._
+  import types._
+  import sizeExtensions._
+  import lexer.escapedChars
+
+  private val argRegs = List(DI, SI, DX, CX, R8, R9)
+
+  private val _7_BIT_MASK = 0x7f
+
+  extension [T](chain: Chain[T])
+    def +(item: T): Chain[T] = chain.append(item)
+
+    /** Concatenates multiple `Chain[T]` instances into a single `Chain[T]`, appending them to the
+      * current `Chain`.
+      *
+      * @param chains
+      *   A variable number of `Chain[T]` instances to concatenate.
+      * @return
+      *   A new `Chain[T]` containing all elements from `chain` concatenated with `chains`.
+      */
+    def concatAll(chains: Chain[T]*): Chain[T] =
+      chains.foldLeft(chain)(_ ++ _)
+
+  def generateAsm(microProg: Program): Chain[AsmLine] = {
+    given stack: Stack = Stack()
+    given labelGenerator: LabelGenerator = LabelGenerator()
+    val Program(funcs, main) = microProg
+
+    val mainLabel = LabelDef("main")
+    val mainAsm = labelGenerator.getDebugFunc(microProg.pos, "main", mainLabel) + mainLabel
+    val progAsm = mainAsm.concatAll(
+      funcPrologue(),
+      main.foldMap(generateStmt(_)),
+      Chain.one(Xor(RAX, RAX)),
+      funcEpilogue(),
+      Chain(Directive.Size(mainLabel, SizeExpr.Relative(mainLabel)), Directive.EndFunc),
+      generateBuiltInFuncs(),
+      RuntimeError.all.foldMap(_.generate),
+      funcs.foldMap(generateUserFunc(_))
+    )
+
+    Chain(
+      Directive.IntelSyntax,
+      Directive.Global("main"),
+      Directive.RoData
+    ).concatAll(
+      labelGenerator.generateDebug,
+      labelGenerator.generateConstants,
+      Chain.one(Directive.Text),
+      progAsm
+    )
+  }
+
+  private def wrapBuiltinFunc(builtin: Builtin, funcBody: Chain[AsmLine])(using
+      stack: Stack,
+      labelGenerator: LabelGenerator
+  ): Chain[AsmLine] = {
+    var asm = Chain.one[AsmLine](labelGenerator.getLabelDef(builtin))
+    asm ++= funcPrologue()
+    asm ++= funcBody
+    asm ++= funcEpilogue()
+    asm
+  }
+
+  private def generateUserFunc(func: FuncDecl)(using
+      labelGenerator: LabelGenerator
+  ): Chain[AsmLine] = {
+    given stack: Stack = Stack()
+    // Setup the stack with param 7 and up
+    func.params.drop(argRegs.size).foreach(stack.reserve(_))
+    stack.reserve(Size.Q64) // Reserve return pointer slot
+    val funcLabel = labelGenerator.getLabelDef(func.name)
+    var asm = labelGenerator.getDebugFunc(func.pos, func.name.name, funcLabel)
+    val debugFunc = asm.size > 0
+    asm += funcLabel
+    asm ++= funcPrologue()
+    // Push the rest of params onto the stack for simplicity
+    argRegs.zip(func.params).foreach { (reg, param) =>
+      asm += stack.push(param, Register(Size.Q64, reg))
+    }
+    asm ++= func.body.foldMap(generateStmt(_))
+    // No need for epilogue here since all user functions must return explicitly
+    if (debugFunc) {
+      asm += Directive.Size(funcLabel, SizeExpr.Relative(funcLabel))
+      asm += Directive.EndFunc
+    }
+    asm
+  }
+
+  private def generateBuiltInFuncs()(using
+      stack: Stack,
+      labelGenerator: LabelGenerator
+  ): Chain[AsmLine] = {
+    var asm = Chain.empty[AsmLine]
+
+    asm ++= wrapBuiltinFunc(
+      Builtin.Exit,
+      Chain(stackAlign, assemblyIR.Call(CLibFunc.Exit))
+    )
+
+    asm ++= wrapBuiltinFunc(
+      Builtin.Printf,
+      Chain(
+        stackAlign,
+        assemblyIR.Call(CLibFunc.PrintF),
+        Xor(RDI, RDI),
+        assemblyIR.Call(CLibFunc.Fflush)
+      )
+    )
+
+    asm ++= wrapBuiltinFunc(
+      Builtin.PrintCharArray,
+      Chain(
+        stackAlign,
+        Load(RDX, MemLocation(RSI, KnownType.Int.size.toInt)),
+        Move(Register(KnownType.Int.size, SI), MemLocation(RSI, opSize = Some(KnownType.Int.size))),
+        assemblyIR.Call(CLibFunc.PrintF),
+        Xor(RDI, RDI),
+        assemblyIR.Call(CLibFunc.Fflush)
+      )
+    )
+
+    asm ++= wrapBuiltinFunc(
+      Builtin.Malloc,
+      Chain(
+        stackAlign,
+        assemblyIR.Call(CLibFunc.Malloc),
+        // Out of memory check
+        Compare(RAX, ImmediateVal(0)),
+        Jump(labelGenerator.getLabelArg(OutOfMemoryError), Cond.Equal)
+      )
+    )
+
+    asm ++= wrapBuiltinFunc(
+      Builtin.Free,
+      Chain(
+        stackAlign,
+        Compare(RDI, ImmediateVal(0)),
+        Jump(labelGenerator.getLabelArg(NullPtrError), Cond.Equal),
+        assemblyIR.Call(CLibFunc.Free)
+      )
+    )
+
+    asm ++= wrapBuiltinFunc(
+      Builtin.Read,
+      Chain(
+        stackAlign,
+        Subtract(Register(Size.Q64, SP), ImmediateVal(8)),
+        Push(RSI),
+        Load(RSI, MemLocation(Register(Size.Q64, SP), opSize = Some(Size.Q64))),
+        assemblyIR.Call(CLibFunc.Scanf),
+        Pop(RAX)
+      )
+    )
+
+    asm
+  }
+
+  private def generateStmt(stmt: Stmt)(using
+      stack: Stack,
+      labelGenerator: LabelGenerator
+  ): Chain[AsmLine] = {
+    val fileNo = labelGenerator.getDebugFile(stmt.pos.file)
+    var asm = Chain.one[AsmLine](Directive.Location(fileNo, stmt.pos.line, None))
+    stmt match {
+      case Assign(lhs, rhs) =>
+        lhs match {
+          case ident: Ident =>
+            if (!stack.contains(ident)) asm += stack.reserve(ident)
+            asm ++= evalExprOntoStack(rhs)
+            asm += stack.pop(RAX)
+            asm += Move(stack.accessVar(ident).copy(opSize = Some(Size.Q64)), RAX)
+          case ArrayElem(x, i) =>
+            asm ++= evalExprOntoStack(rhs)
+            asm ++= evalExprOntoStack(i)
+            asm += stack.pop(RCX)
+            asm += Compare(ECX, ImmediateVal(0))
+            asm += Jump(labelGenerator.getLabelArg(OutOfBoundsError), Cond.Less)
+            asm += stack.push(KnownType.Int.size, RCX)
+            asm ++= evalExprOntoStack(x)
+            asm += stack.pop(RAX)
+            asm += stack.pop(RCX)
+            asm += Compare(RAX, ImmediateVal(0))
+            asm += Jump(labelGenerator.getLabelArg(NullPtrError), Cond.Equal)
+            asm += Compare(MemLocation(RAX, opSize = Some(KnownType.Int.size)), ECX)
+            asm += Jump(labelGenerator.getLabelArg(OutOfBoundsError), Cond.LessEqual)
+            asm += stack.pop(RDX)
+
+            asm += Move(
+              MemLocation(RAX, KnownType.Int.size.toInt, (RCX, x.ty.elemSize.toInt)),
+              Register(x.ty.elemSize, DX)
+            )
+        }
+
+      case If(cond, thenBranch, elseBranch) =>
+        val elseLabel = labelGenerator.getLabel()
+        val endLabel = labelGenerator.getLabel()
+
+        asm ++= evalExprOntoStack(cond)
+        asm += stack.pop(RAX)
+        asm += Compare(RAX, ImmediateVal(0))
+        asm += Jump(LabelArg(elseLabel), Cond.Equal)
+
+        asm ++= stack.withScope(() => thenBranch.foldMap(generateStmt))
+        asm += Jump(LabelArg(endLabel))
+        asm += LabelDef(elseLabel)
+
+        asm ++= stack.withScope(() => elseBranch.foldMap(generateStmt))
+        asm += LabelDef(endLabel)
+
+      case While(cond, body) =>
+        val startLabel = labelGenerator.getLabel()
+        val endLabel = labelGenerator.getLabel()
+
+        asm += LabelDef(startLabel)
+        asm ++= evalExprOntoStack(cond)
+        asm += stack.pop(RAX)
+        asm += Compare(RAX, ImmediateVal(0))
+        asm += Jump(LabelArg(endLabel), Cond.Equal)
+
+        asm ++= stack.withScope(() => body.foldMap(generateStmt))
+        asm += Jump(LabelArg(startLabel))
+        asm += LabelDef(endLabel)
+
+      case call: microWacc.Call =>
+        asm ++= generateCall(call, isTail = false)
+
+      case microWacc.Return(expr) =>
+        expr match {
+          case call: microWacc.Call =>
+            asm ++= generateCall(call, isTail = true) // tco
+          case _ =>
+            asm ++= evalExprOntoStack(expr)
+            asm += stack.pop(RAX)
+            asm ++= funcEpilogue()
+        }
+    }
+
+    asm
+  }
+
+  private def evalExprOntoStack(expr: Expr)(using
+      stack: Stack,
+      labelGenerator: LabelGenerator
+  ): Chain[AsmLine] = {
+    var asm = Chain.empty[AsmLine]
+    val stackSizeStart = stack.size
+    expr match {
+      case IntLiter(v)  => asm += stack.push(KnownType.Int.size, ImmediateVal(v))
+      case CharLiter(v) => asm += stack.push(KnownType.Char.size, ImmediateVal(v.toInt))
+      case ident: Ident =>
+        val location = stack.accessVar(ident)
+        // items in stack are guaranteed to be in Q64 slots,
+        // so we are safe to wipe the opSize from the memory location
+        asm += stack.push(ident.ty.size, location.copy(opSize = None))
+
+      case array @ ArrayLiter(elems) =>
+        expr.ty match {
+          case KnownType.String =>
+            val str = elems.collect { case CharLiter(v) => v }.mkString
+            asm += Load(RAX, MemLocation(RIP, labelGenerator.getLabelArg(str)))
+            asm += stack.push(KnownType.String.size, RAX)
+          case ty =>
+            asm ++= generateCall(
+              microWacc.Call(Builtin.Malloc, List(IntLiter(array.heapSize)))(array.pos),
+              isTail = false
+            )
+            asm += stack.push(KnownType.Array(?).size, RAX)
+            // Store the length of the array at the start
+            asm += Move(
+              MemLocation(RAX, opSize = Some(KnownType.Int.size)),
+              ImmediateVal(elems.size)
+            )
+            elems.zipWithIndex.foldMap { (elem, i) =>
+              asm ++= evalExprOntoStack(elem)
+              asm += stack.pop(RCX)
+              asm += stack.pop(RAX)
+              asm += Move(
+                MemLocation(RAX, KnownType.Int.size.toInt + i * ty.elemSize.toInt),
+                Register(ty.elemSize, CX)
+              )
+              asm += stack.push(KnownType.Array(?).size, RAX)
+            }
+        }
+
+      case BoolLiter(true) =>
+        asm += stack.push(KnownType.Bool.size, ImmediateVal(1))
+      case BoolLiter(false) =>
+        asm += Xor(RAX, RAX)
+        asm += stack.push(KnownType.Bool.size, RAX)
+      case NullLiter() =>
+        asm += stack.push(KnownType.Pair(?, ?).size, ImmediateVal(0))
+      case ArrayElem(x, i) =>
+        asm ++= evalExprOntoStack(x)
+        asm ++= evalExprOntoStack(i)
+        asm += stack.pop(RCX)
+        asm += Compare(RCX, ImmediateVal(0))
+        asm += Jump(labelGenerator.getLabelArg(OutOfBoundsError), Cond.Less)
+        asm += stack.pop(RAX)
+        asm += Compare(RAX, ImmediateVal(0))
+        asm += Jump(labelGenerator.getLabelArg(NullPtrError), Cond.Equal)
+        asm += Compare(MemLocation(RAX, opSize = Some(KnownType.Int.size)), ECX)
+        asm += Jump(labelGenerator.getLabelArg(OutOfBoundsError), Cond.LessEqual)
+        // + Int because we store the length of the array at the start
+        asm += Move(
+          Register(x.ty.elemSize, AX),
+          MemLocation(RAX, KnownType.Int.size.toInt, (RCX, x.ty.elemSize.toInt))
+        )
+        asm += stack.push(x.ty.elemSize, RAX)
+      case UnaryOp(x, op) =>
+        asm ++= evalExprOntoStack(x)
+        op match {
+          case UnaryOperator.Chr =>
+            asm += Move(EAX, stack.head)
+            asm += And(EAX, ImmediateVal(~_7_BIT_MASK))
+            asm += Compare(EAX, ImmediateVal(0))
+            asm += Jump(labelGenerator.getLabelArg(BadChrError), Cond.NotEqual)
+          case UnaryOperator.Ord => // No op needed
+          case UnaryOperator.Len =>
+            asm += stack.pop(RAX)
+            asm += Move(EAX, MemLocation(RAX, opSize = Some(KnownType.Int.size)))
+            asm += stack.push(KnownType.Int.size, RAX)
+          case UnaryOperator.Negate =>
+            asm += Xor(EAX, EAX)
+            asm += Subtract(EAX, stack.head)
+            asm += Jump(labelGenerator.getLabelArg(OverflowError), Cond.Overflow)
+            asm += stack.drop()
+            asm += stack.push(KnownType.Int.size, RAX)
+          case UnaryOperator.Not =>
+            asm += Xor(stack.head, ImmediateVal(1))
+        }
+
+      case BinaryOp(x, y, op) =>
+        val destX = Register(x.ty.size, AX)
+        asm ++= evalExprOntoStack(y)
+        asm ++= evalExprOntoStack(x)
+        asm += stack.pop(RAX)
+
+        op match {
+          case BinaryOperator.Add =>
+            asm += Add(stack.head, destX)
+            asm += Jump(labelGenerator.getLabelArg(OverflowError), Cond.Overflow)
+          case BinaryOperator.Sub =>
+            asm += Subtract(destX, stack.head)
+            asm += Jump(labelGenerator.getLabelArg(OverflowError), Cond.Overflow)
+            asm += stack.drop()
+            asm += stack.push(destX.size, RAX)
+          case BinaryOperator.Mul =>
+            asm += Multiply(destX, stack.head)
+            asm += Jump(labelGenerator.getLabelArg(OverflowError), Cond.Overflow)
+            asm += stack.drop()
+            asm += stack.push(destX.size, RAX)
+
+          case BinaryOperator.Div =>
+            asm += Compare(stack.head, ImmediateVal(0))
+            asm += Jump(labelGenerator.getLabelArg(ZeroDivError), Cond.Equal)
+            asm += CDQ()
+            asm += Divide(stack.head)
+            asm += stack.drop()
+            asm += stack.push(destX.size, RAX)
+
+          case BinaryOperator.Mod =>
+            asm += Compare(stack.head, ImmediateVal(0))
+            asm += Jump(labelGenerator.getLabelArg(ZeroDivError), Cond.Equal)
+            asm += CDQ()
+            asm += Divide(stack.head)
+            asm += stack.drop()
+            asm += stack.push(destX.size, RDX)
+
+          case BinaryOperator.Eq        => asm ++= generateComparison(destX, Cond.Equal)
+          case BinaryOperator.Neq       => asm ++= generateComparison(destX, Cond.NotEqual)
+          case BinaryOperator.Greater   => asm ++= generateComparison(destX, Cond.Greater)
+          case BinaryOperator.GreaterEq => asm ++= generateComparison(destX, Cond.GreaterEqual)
+          case BinaryOperator.Less      => asm ++= generateComparison(destX, Cond.Less)
+          case BinaryOperator.LessEq    => asm ++= generateComparison(destX, Cond.LessEqual)
+          case BinaryOperator.And       => asm += And(stack.head, destX)
+          case BinaryOperator.Or        => asm += Or(stack.head, destX)
+        }
+
+      case call: microWacc.Call =>
+        asm ++= generateCall(call, isTail = false)
+        asm += stack.push(call.ty.size, RAX)
+    }
+
+    assert(
+      stack.size == stackSizeStart + 1,
+      "Sanity check: ONLY the evaluated expression should have been pushed onto the stack"
+    )
+    asm ++= zeroRest(stack.head.copy(opSize = Some(Size.Q64)), expr.ty.size)
+    asm
+  }
+
+  private def generateCall(call: microWacc.Call, isTail: Boolean)(using
+      stack: Stack,
+      labelGenerator: LabelGenerator
+  ): Chain[AsmLine] = {
+    var asm = Chain.empty[AsmLine]
+    val microWacc.Call(target, args) = call
+
+    // Evaluate arguments 0-6
+    argRegs
+      .zip(args)
+      .map { (reg, expr) =>
+        asm ++= evalExprOntoStack(expr)
+        reg
+      }
+      // And set the appropriate registers
+      .reverse
+      .foreach { reg =>
+        asm += stack.pop(Register(Size.Q64, reg))
+      }
+
+    // Evaluate arguments 7 and up and push them onto the stack
+    args.drop(argRegs.size).foldMap {
+      asm ++= evalExprOntoStack(_)
+    }
+
+    // Tail Call Optimisation (TCO)
+    if (isTail) {
+      asm += Jump(labelGenerator.getLabelArg(target)) // tail call
+    } else {
+      asm += assemblyIR.Call(labelGenerator.getLabelArg(target)) // regular call
+    }
+
+    // Remove arguments 7 and up from the stack
+    if (args.size > argRegs.size) {
+      asm += stack.drop(args.size - argRegs.size)
+    }
+
+    asm
+  }
+
+  private def generateComparison(destX: Register, cond: Cond)(using
+      stack: Stack
+  ): Chain[AsmLine] = {
+    var asm = Chain.empty[AsmLine]
+
+    asm += Compare(destX, stack.head)
+    asm += Set(Register(Size.B8, AX), cond)
+    asm ++= zeroRest(RAX, Size.B8)
+    asm += stack.drop()
+    asm += stack.push(Size.B8, RAX)
+
+    asm
+  }
+
+  private def funcPrologue()(using stack: Stack): Chain[AsmLine] = {
+    var asm = Chain.empty[AsmLine]
+    asm += stack.push(Size.Q64, RBP)
+    asm += Move(RBP, Register(Size.Q64, SP))
+    asm
+  }
+
+  private def funcEpilogue(): Chain[AsmLine] = {
+    var asm = Chain.empty[AsmLine]
+    asm += Move(Register(Size.Q64, SP), RBP)
+    asm += Pop(RBP)
+    asm += assemblyIR.Return()
+    asm
+  }
+
+  def stackAlign: AsmLine = And(Register(Size.Q64, SP), ImmediateVal(-16))
+  private def zeroRest(dest: Dest, size: Size): Chain[AsmLine] = size match {
+    case Size.Q64 | Size.D32 => Chain.empty
+    case _                   => Chain.one(And(dest, ImmediateVal((1 << (size.toInt * 8)) - 1)))
+  }
+
+  private val escapedCharsMapping = escapedChars.map { case (k, v) => v -> s"\\$k" }
+  extension (s: String) {
+    def escaped: String =
+      s.flatMap(c => escapedCharsMapping.getOrElse(c, c.toString))
+  }
+}

src/main/wacc/backend/assemblyIR.scala

@@ -0,0 +1,272 @@
+package wacc
+
+object assemblyIR {
+
+  sealed trait AsmLine
+  sealed trait Operand
+  sealed trait Src extends Operand // mem location, register and imm value
+  sealed trait Dest extends Operand // mem location and register
+
+  enum Size {
+    case Q64, D32, W16, B8
+
+    def toInt: Int = this match {
+      case Q64 => 8
+      case D32 => 4
+      case W16 => 2
+      case B8  => 1
+    }
+
+    private val ptr = "ptr "
+
+    override def toString(): String = this match {
+      case Q64 => "qword " + ptr
+      case D32 => "dword " + ptr
+      case W16 => "word " + ptr
+      case B8  => "byte " + ptr
+    }
+  }
+
+  enum RegName {
+    case AX, BX, CX, DX, SI, DI, SP, BP, IP, R8, R9, R10, R11, R12, R13, R14, R15
+  }
+
+  case class Register(size: Size, name: RegName) extends Dest with Src {
+    import RegName._
+
+    if (size == Size.B8 && name == RegName.IP) {
+      throw new IllegalArgumentException("Cannot have 8 bit register for IP")
+    }
+    override def toString = name match {
+      case AX  => tradToString("ax", "al")
+      case BX  => tradToString("bx", "bl")
+      case CX  => tradToString("cx", "cl")
+      case DX  => tradToString("dx", "dl")
+      case SI  => tradToString("si", "sil")
+      case DI  => tradToString("di", "dil")
+      case SP  => tradToString("sp", "spl")
+      case BP  => tradToString("bp", "bpl")
+      case IP  => tradToString("ip", "#INVALID")
+      case R8  => newToString(8)
+      case R9  => newToString(9)
+      case R10 => newToString(10)
+      case R11 => newToString(11)
+      case R12 => newToString(12)
+      case R13 => newToString(13)
+      case R14 => newToString(14)
+      case R15 => newToString(15)
+    }
+
+    private def tradToString(base: String, byteName: String): String =
+      size match {
+        case Size.Q64 => "r" + base
+        case Size.D32 => "e" + base
+        case Size.W16 => base
+        case Size.B8  => byteName
+      }
+
+    private def newToString(base: Int): String = {
+      val b = base.toString
+      "r" + (size match {
+        case Size.Q64 => b
+        case Size.D32 => b + "d"
+        case Size.W16 => b + "w"
+        case Size.B8  => b + "b"
+      })
+    }
+  }
+
+  // arguments
+  enum CLibFunc extends Operand {
+    case Scanf,
+      Fflush,
+      Exit,
+      PrintF,
+      Malloc,
+      Free
+
+    private val plt = "@plt"
+
+    override def toString = this match {
+      case Scanf  => "scanf" + plt
+      case Fflush => "fflush" + plt
+      case Exit   => "exit" + plt
+      case PrintF => "printf" + plt
+      case Malloc => "malloc" + plt
+      case Free   => "free" + plt
+    }
+  }
+
+  case class MemLocation(
+      base: Register,
+      offset: Int | LabelArg = 0,
+      // scale 0 will make register irrelevant, no other reason as to why it's RAX
+      scaledIndex: (Register, Int) = (Register(Size.Q64, RegName.AX), 0),
+      opSize: Option[Size] = None
+  ) extends Dest
+      with Src {
+    def copy(
+        base: Register = this.base,
+        offset: Int | LabelArg = this.offset,
+        scaledIndex: (Register, Int) = this.scaledIndex,
+        opSize: Option[Size] = this.opSize
+    ): MemLocation = MemLocation(base, offset, scaledIndex, opSize)
+
+    override def toString(): String = {
+      val opSizeStr = opSize.map(_.toString).getOrElse("")
+      val baseStr = base.toString
+      val offsetStr = offset match {
+        case 0   => ""
+        case off => s" + $off"
+      }
+      val scaledIndexStr = scaledIndex match {
+        case (reg, scale) if scale != 0 => s" + $reg * $scale"
+        case _                          => ""
+      }
+      s"$opSizeStr[$baseStr$scaledIndexStr$offsetStr]"
+    }
+  }
+
+  case class ImmediateVal(value: Int) extends Src {
+    override def toString = value.toString
+  }
+
+  case class LabelArg(name: String) extends Operand {
+    override def toString = name
+  }
+
+  abstract class Operation(ins: String, ops: Operand*) extends AsmLine {
+    override def toString: String = s"\t$ins ${ops.mkString(", ")}"
+  }
+
+  // arithmetic operations
+  case class Add(op1: Dest, op2: Src) extends Operation("add", op1, op2)
+  case class Subtract(op1: Dest, op2: Src) extends Operation("sub", op1, op2)
+  case class Multiply(ops: Operand*) extends Operation("imul", ops*)
+  case class Divide(op1: Src) extends Operation("idiv", op1)
+  case class Negate(op: Dest) extends Operation("neg", op)
+  // bitwise operations
+  case class And(op1: Dest, op2: Src) extends Operation("and", op1, op2)
+  case class Or(op1: Dest, op2: Src) extends Operation("or", op1, op2)
+  case class Xor(op1: Dest, op2: Src) extends Operation("xor", op1, op2)
+  case class Compare(op1: Dest, op2: Src) extends Operation("cmp", op1, op2)
+  case class CDQ() extends Operation("cdq")
+  // stack operations
+  case class Push(op1: Src) extends Operation("push", op1)
+  case class Pop(op1: Src) extends Operation("pop", op1)
+  // move operations
+  case class Move(op1: Dest, op2: Src) extends Operation("mov", op1, op2)
+  case class Load(op1: Register, op2: MemLocation) extends Operation("lea ", op1, op2)
+
+  // function call operations
+  case class Call(op1: CLibFunc | LabelArg) extends Operation("call", op1)
+  case class Return() extends Operation("ret")
+
+  // conditional operations
+  case class Jump(op1: LabelArg, condition: Cond = Cond.Always)
+      extends Operation(s"j${condition.toString}", op1)
+  case class Set(op1: Dest, condition: Cond = Cond.Always)
+      extends Operation(s"set${condition.toString}", op1)
+
+  case class LabelDef(name: String) extends AsmLine {
+    override def toString = s"$name:"
+  }
+
+  case class Comment(comment: String) extends AsmLine {
+    override def toString =
+      comment.split("\n").map(line => s"# ${line}").mkString("\n")
+  }
+
+  enum Cond {
+    case Equal,
+      NotEqual,
+      Greater,
+      GreaterEqual,
+      Less,
+      LessEqual,
+      Overflow,
+      Always
+    override def toString(): String = this match {
+      case Equal        => "e"
+      case NotEqual     => "ne"
+      case Greater      => "g"
+      case GreaterEqual => "ge"
+      case Less         => "l"
+      case LessEqual    => "le"
+      case Overflow     => "o"
+      case Always       => "mp"
+    }
+  }
+
+  enum Directive extends AsmLine {
+    case IntelSyntax, RoData, Text, EndFunc
+    case Global(name: String)
+    case Int(value: scala.Int)
+    case Asciz(string: String)
+    case File(no: scala.Int, file: String)
+    case Location(fileNo: scala.Int, lineNo: scala.Int, colNo: Option[scala.Int])
+    case Func(name: String, label: LabelDef)
+    case Type(label: LabelDef, symbolType: SymbolType)
+    case Size(label: LabelDef, expr: SizeExpr)
+
+    override def toString(): String = this match {
+      case IntelSyntax    => ".intel_syntax noprefix"
+      case Global(name)   => s".globl $name"
+      case Text           => ".text"
+      case RoData         => ".section .rodata"
+      case Int(value)     => s"\t.int $value"
+      case Asciz(string)  => s"\t.asciz \"$string\""
+      case File(no, file) => s".file $no \"${file}\""
+      case Location(fileNo, lineNo, colNo) =>
+        s"\t.loc $fileNo $lineNo" + colNo.map(c => s" $c").getOrElse("")
+      case Func(name, label) =>
+        s".func $name, ${label.name}"
+      case EndFunc => ".endfunc"
+      case Type(label, symbolType) =>
+        s".type ${label.name}, @${symbolType.toString}"
+      case Directive.Size(label, expr) =>
+        s".size ${label.name}, ${expr.toString}"
+    }
+  }
+
+  enum SymbolType {
+    case Function
+
+    override def toString(): String = this match {
+      case Function => "function"
+    }
+  }
+
+  enum SizeExpr {
+    case Relative(label: LabelDef)
+
+    override def toString(): String = this match {
+      case Relative(label) => s".-${label.name}"
+    }
+  }
+
+  enum PrintFormat {
+    case Int, Char, String
+
+    override def toString(): String = this match {
+      case Int    => "%d"
+      case Char   => "%c"
+      case String => "%s"
+    }
+  }
+
+  object commonRegisters {
+    import Size._
+    import RegName._
+
+    val RAX = Register(Q64, AX)
+    val EAX = Register(D32, AX)
+    val RDI = Register(Q64, DI)
+    val RIP = Register(Q64, IP)
+    val RBP = Register(Q64, BP)
+    val RSI = Register(Q64, SI)
+    val RDX = Register(Q64, DX)
+    val RCX = Register(Q64, CX)
+    val ECX = Register(D32, CX)
+  }
+}

src/main/wacc/backend/sizeExtensions.scala

@@ -0,0 +1,33 @@
+package wacc
+
+object sizeExtensions {
+  import microWacc._
+  import types._
+  import assemblyIR.Size
+
+  extension (expr: Expr) {
+
+    /** Calculate the size (bytes) of the heap required for the expression. */
+    def heapSize: Int = (expr, expr.ty) match {
+      case (ArrayLiter(elems), ty) =>
+        KnownType.Int.size.toInt + elems.size * ty.elemSize.toInt
+      case _ => expr.ty.size.toInt
+    }
+  }
+
+  extension (ty: SemType) {
+
+    /** Calculate the size (bytes) of a type in a register. */
+    def size: Size = ty match {
+      case KnownType.Int                                                    => Size.D32
+      case KnownType.Bool | KnownType.Char                                  => Size.B8
+      case KnownType.String | KnownType.Array(_) | KnownType.Pair(_, _) | ? => Size.Q64
+    }
+
+    def elemSize: Size = ty match {
+      case KnownType.Array(elem) => elem.size
+      case KnownType.Pair(_, _)  => Size.Q64
+      case _                     => ty.size
+    }
+  }
+}

src/main/wacc/backend/writer.scala

@@ -0,0 +1,42 @@
+package wacc
+
+import cats.effect.Resource
+import java.nio.charset.StandardCharsets
+import java.io.BufferedWriter
+import java.io.FileWriter
+import cats.data.Chain
+import cats.effect.IO
+
+import org.typelevel.log4cats.Logger
+import java.nio.file.Path
+
+object writer {
+  import assemblyIR._
+
+  // TODO: Judging from documentation it seems as though IO.blocking is the correct choice
+  // But needs checking
+
+  /** Creates a resource safe BufferedWriter */
+  private def bufferedWriter(outputPath: Path): Resource[IO, BufferedWriter] =
+    Resource.make {
+      IO.blocking(new BufferedWriter(new FileWriter(outputPath.toFile, StandardCharsets.UTF_8)))
+    } { writer =>
+      IO.blocking(writer.close())
+        .handleErrorWith(_ => IO.unit) // TODO: ensures writer is closed even if an error occurs
+    }
+
+  /** Write line safely into a BufferedWriter */
+  private def writeLines(writer: BufferedWriter, lines: Chain[AsmLine]): IO[Unit] =
+    IO.blocking {
+      lines.iterator.foreach { line =>
+        writer.write(line.toString)
+        writer.newLine()
+      }
+    }
+
+  /** Main function to write assembly to a file */
+  def writeTo(asmList: Chain[AsmLine], outputPath: Path)(using logger: Logger[IO]): IO[Unit] =
+    bufferedWriter(outputPath).use {
+      writeLines(_, asmList)
+    }
+}

src/main/wacc/frontend/Error.scala

@@ -0,0 +1,126 @@
+package wacc
+
+import wacc.ast.Position
+import wacc.types._
+import java.io.File
+
+private val SYNTAX_ERROR = 100
+private val SEMANTIC_ERROR = 200
+
+/** Error types for semantic errors
+  */
+enum Error {
+  case DuplicateDeclaration(ident: ast.Ident)
+  case UndeclaredVariable(ident: ast.Ident)
+  case UndefinedFunction(ident: ast.Ident)
+
+  case FunctionParamsMismatch(ident: ast.Ident, expected: Int, got: Int, funcType: FuncType)
+  case SemanticError(pos: Position, msg: String)
+  case TypeMismatch(pos: Position, expected: SemType, got: SemType, msg: String)
+  case InternalError(pos: Position, msg: String)
+
+  case SyntaxError(file: File, msg: String)
+}
+
+extension (e: Error) {
+  def exitCode: Int = e match {
+    case Error.SyntaxError(_, _) => SYNTAX_ERROR
+    case _                       => SEMANTIC_ERROR
+  }
+}
+
+/** Function to handle printing the details of a given semantic error
+  *
+  * @param error
+  *   Error object
+  * @param errorContent
+  *   Contents of the file to generate code snippets
+  */
+def formatError(error: Error): String = {
+  val sb = new StringBuilder()
+
+  /** Format the file of an error
+    *
+    * @param file
+    *   File of the error
+    */
+  def formatFile(file: File): Unit = {
+    sb.append(s"File: ${file.getCanonicalPath}\n")
+  }
+
+  /** Function to format the position of an error
+    *
+    * @param pos
+    *   Position of the error
+    */
+  def formatPosition(pos: Position): Unit = {
+    formatFile(pos.file)
+    sb.append(s"(line ${pos.line}, column ${pos.column}):\n")
+  }
+
+  /** Function to highlight a section of code for an error message
+    *
+    * @param pos
+    *   Position of the error
+    * @param size
+    *   Size(in chars) of section to highlight
+    */
+  def formatHighlight(pos: Position, size: Int): Unit = {
+    val lines = os.read(os.Path(pos.file.getCanonicalPath)).split("\n")
+    val preLine = if (pos.line > 1) lines(pos.line - 2) else ""
+    val midLine = lines(pos.line - 1)
+    val postLine = if (pos.line < lines.size) lines(pos.line) else ""
+    val linePointer = " " * (pos.column + 2) + ("^" * (size)) + "\n"
+
+    sb.append(
+      s"  >$preLine\n  >$midLine\n$linePointer  >$postLine\netscape"
+    )
+  }
+
+  error match {
+    case Error.SyntaxError(_, _) =>
+      sb.append("Syntax error:\n")
+    case _ =>
+      sb.append("Semantic error:\n")
+  }
+
+  error match {
+    case Error.DuplicateDeclaration(ident) =>
+      formatPosition(ident.pos)
+      sb.append(s"Duplicate declaration of identifier ${ident.v}\n")
+      formatHighlight(ident.pos, ident.v.length)
+    case Error.UndeclaredVariable(ident) =>
+      formatPosition(ident.pos)
+      sb.append(s"Undeclared variable ${ident.v}\n")
+      formatHighlight(ident.pos, ident.v.length)
+    case Error.UndefinedFunction(ident) =>
+      formatPosition(ident.pos)
+      sb.append(s"Undefined function ${ident.v}\n")
+      formatHighlight(ident.pos, ident.v.length)
+    case Error.FunctionParamsMismatch(id, expected, got, funcType) =>
+      formatPosition(id.pos)
+      sb.append(s"Function expects $expected parameters, got $got\n")
+      sb.append(
+        s"(function ${id.v} has type (${funcType.params.mkString(", ")}) -> ${funcType.returnType})\n"
+      )
+      formatHighlight(id.pos, 1)
+    case Error.TypeMismatch(pos, expected, got, msg) =>
+      formatPosition(pos)
+      sb.append(s"Type mismatch: $msg\nExpected: $expected\nGot: $got\n")
+      formatHighlight(pos, 1)
+    case Error.SemanticError(pos, msg) =>
+      formatPosition(pos)
+      sb.append(msg + "\n")
+      formatHighlight(pos, 1)
+    case wacc.Error.InternalError(pos, msg) =>
+      formatPosition(pos)
+      sb.append(s"Internal error: $msg\n")
+      formatHighlight(pos, 1)
+    case Error.SyntaxError(file, msg) =>
+      formatFile(file)
+      sb.append(msg + "\n")
+      sb.append("\n")
+  }
+
+  sb.toString()
+}

src/main/wacc/frontend/ast.scala

@@ -1,10 +1,10 @@
 package wacc
 
+import java.io.File
 import parsley.Parsley
 import parsley.generic.ErrorBridge
 import parsley.ap._
 import parsley.position._
-import parsley.syntax.zipped._
 import cats.data.NonEmptyList
 
 object ast {
@@ -23,26 +23,42 @@ object ast {
   /* ============================ ATOMIC EXPRESSIONS ============================ */
 
   case class IntLiter(v: Int)(val pos: Position) extends Expr6
-  object IntLiter extends ParserBridgePos1[Int, IntLiter]
+  object IntLiter extends ParserBridgePos1Atom[Int, IntLiter]
   case class BoolLiter(v: Boolean)(val pos: Position) extends Expr6
-  object BoolLiter extends ParserBridgePos1[Boolean, BoolLiter]
+  object BoolLiter extends ParserBridgePos1Atom[Boolean, BoolLiter]
   case class CharLiter(v: Char)(val pos: Position) extends Expr6
-  object CharLiter extends ParserBridgePos1[Char, CharLiter]
+  object CharLiter extends ParserBridgePos1Atom[Char, CharLiter]
   case class StrLiter(v: String)(val pos: Position) extends Expr6
-  object StrLiter extends ParserBridgePos1[String, StrLiter]
+  object StrLiter extends ParserBridgePos1Atom[String, StrLiter]
   case class PairLiter()(val pos: Position) extends Expr6
   object PairLiter extends ParserBridgePos0[PairLiter]
-  case class Ident(v: String, var uid: Int = -1)(val pos: Position) extends Expr6 with LValue
-  object Ident extends ParserBridgePos1[String, Ident] {
+  case class Ident(var v: String, var guid: Int = -1, var ty: types.RenamerType = types.?)(
+      val pos: Position
+  ) extends Expr6
+      with LValue
+  object Ident extends ParserBridgePos1Atom[String, Ident] {
     def apply(v: String)(pos: Position): Ident = new Ident(v)(pos)
   }
   case class ArrayElem(name: Ident, indices: NonEmptyList[Expr])(val pos: Position)
       extends Expr6
       with LValue
-  object ArrayElem extends ParserBridgePos1[NonEmptyList[Expr], Ident => ArrayElem] {
-    def apply(a: NonEmptyList[Expr])(pos: Position): Ident => ArrayElem =
-      name => ArrayElem(name, a)(pos)
+  object ArrayElem extends ParserBridgePos2Chain[NonEmptyList[Expr], Ident, ArrayElem] {
+    def apply(indices: NonEmptyList[Expr], name: Ident)(pos: Position): ArrayElem =
+      new ArrayElem(name, indices)(pos)
   }
+  // object ArrayElem extends ParserBridgePos1[NonEmptyList[Expr], (File => Ident) => ArrayElem] {
+  //   def apply(a: NonEmptyList[Expr])(pos: Position): (File => Ident) => ArrayElem =
+  //     name => ArrayElem(name(pos.file), a)(pos)
+  // }
+  // object ArrayElem extends ParserSingletonBridgePos[(File => NonEmptyList[Expr]) => (File => Ident) => File => ArrayElem] {
+  //   // def apply(indices: NonEmptyList[Expr]): (File => Ident) => File => ArrayElem =
+  //   //   name => file => new ArrayElem(name(file), )
+  //   def apply(indices: Parsley[File => NonEmptyList[Expr]]): Parsley[(File => Ident) => File => ArrayElem] =
+  //     // error(ap1(pos.map(con),))
+
+  //   override final def con(pos: (Int, Int)): (File => NonEmptyList[Expr]) =>  => C =
+  //     (a, b) => file => this.apply(a(file), b(file))(Position(pos._1, pos._2, file))
+  // }
   case class Parens(expr: Expr)(val pos: Position) extends Expr6
   object Parens extends ParserBridgePos1[Expr, Parens]
 
@@ -120,8 +136,9 @@ object ast {
   case class ArrayType(elemType: Type, dimensions: Int)(val pos: Position)
       extends Type
       with PairElemType
-  object ArrayType extends ParserBridgePos1[Int, Type => ArrayType] {
-    def apply(a: Int)(pos: Position): Type => ArrayType = elemType => ArrayType(elemType, a)(pos)
+  object ArrayType extends ParserBridgePos2Chain[Int, Type, ArrayType] {
+    def apply(dimensions: Int, elemType: Type)(pos: Position): ArrayType =
+      ArrayType(elemType, dimensions)(pos)
   }
   case class PairType(fst: PairElemType, snd: PairElemType)(val pos: Position) extends Type
   object PairType extends ParserBridgePos2[PairElemType, PairElemType, PairType]
@@ -132,6 +149,18 @@ object ast {
 
   /* ============================ PROGRAM STRUCTURE ============================ */
 
+  case class ImportedFunc(sourceName: Ident, importName: Ident)(val pos: Position)
+  object ImportedFunc extends ParserBridgePos2[Ident, Option[Ident], ImportedFunc] {
+    def apply(a: Ident, b: Option[Ident])(pos: Position): ImportedFunc =
+      new ImportedFunc(a, b.getOrElse(a))(pos)
+  }
+
+  case class Import(source: StrLiter, funcs: NonEmptyList[ImportedFunc])(val pos: Position)
+  object Import extends ParserBridgePos2[StrLiter, NonEmptyList[ImportedFunc], Import]
+
+  case class PartialProgram(imports: List[Import], self: Program)(val pos: Position)
+  object PartialProgram extends ParserBridgePos2[List[Import], Program, PartialProgram]
+
   case class Program(funcs: List[FuncDecl], main: NonEmptyList[Stmt])(val pos: Position)
   object Program extends ParserBridgePos2[List[FuncDecl], NonEmptyList[Stmt], Program]
 
@@ -144,15 +173,15 @@ object ast {
       body: NonEmptyList[Stmt]
   )(val pos: Position)
   object FuncDecl
-      extends ParserBridgePos2[
-        List[Param],
-        NonEmptyList[Stmt],
-        ((Type, Ident)) => FuncDecl
+      extends ParserBridgePos2Chain[
+        (List[Param], NonEmptyList[Stmt]),
+        ((Type, Ident)),
+        FuncDecl
       ] {
-    def apply(params: List[Param], body: NonEmptyList[Stmt])(
+    def apply(paramsBody: (List[Param], NonEmptyList[Stmt]), retTyName: (Type, Ident))(
         pos: Position
-    ): ((Type, Ident)) => FuncDecl =
-      (returnType, name) => FuncDecl(returnType, name, params, body)(pos)
+    ): FuncDecl =
+      new FuncDecl(retTyName._1, retTyName._2, paramsBody._1, paramsBody._2)(pos)
   }
 
   case class Param(paramType: Type, name: Ident)(val pos: Position)
@@ -160,7 +189,9 @@ object ast {
 
   /* ============================ STATEMENTS ============================ */
 
-  sealed trait Stmt
+  sealed trait Stmt {
+    val pos: Position
+  }
   case class Skip()(val pos: Position) extends Stmt
   object Skip extends ParserBridgePos0[Skip]
   case class VarDecl(varType: Type, name: Ident, value: RValue)(val pos: Position) extends Stmt
@@ -192,7 +223,9 @@ object ast {
     val pos: Position
   }
 
-  sealed trait RValue
+  sealed trait RValue {
+    val pos: Position
+  }
   case class ArrayLiter(elems: List[Expr])(val pos: Position) extends RValue
   object ArrayLiter extends ParserBridgePos1[List[Expr], ArrayLiter]
   case class NewPair(fst: Expr, snd: Expr)(val pos: Position) extends RValue
@@ -208,7 +241,7 @@ object ast {
 
   /* ============================ PARSER BRIDGES ============================ */
 
-  case class Position(line: Int, column: Int)
+  case class Position(line: Int, column: Int, file: File)
 
   trait ParserSingletonBridgePos[+A] extends ErrorBridge {
     protected def con(pos: (Int, Int)): A
@@ -216,38 +249,63 @@ object ast {
     final def <#(op: Parsley[?]): Parsley[A] = this from op
   }
 
-  trait ParserBridgePos0[+A] extends ParserSingletonBridgePos[A] {
+  trait ParserBridgePos0[+A] extends ParserSingletonBridgePos[File => A] {
     def apply()(pos: Position): A
 
-    override final def con(pos: (Int, Int)): A =
-      apply()(Position(pos._1, pos._2))
+    override final def con(pos: (Int, Int)): File => A =
+      file => apply()(Position(pos._1, pos._2, file))
   }
 
-  trait ParserBridgePos1[-A, +B] extends ParserSingletonBridgePos[A => B] {
+  trait ParserBridgePos1Atom[-A, +B] extends ParserSingletonBridgePos[A => File => B] {
     def apply(a: A)(pos: Position): B
-    def apply(a: Parsley[A]): Parsley[B] = error(ap1(pos.map(con), a))
+    def apply(a: Parsley[A]): Parsley[File => B] = error(ap1(pos.map(con), a))
 
-    override final def con(pos: (Int, Int)): A => B =
-      this.apply(_)(Position(pos._1, pos._2))
+    override final def con(pos: (Int, Int)): A => File => B =
+      a => file => this.apply(a)(Position(pos._1, pos._2, file))
   }
 
-  trait ParserBridgePos2[-A, -B, +C] extends ParserSingletonBridgePos[(A, B) => C] {
+  trait ParserBridgePos1[-A, +B] extends ParserSingletonBridgePos[(File => A) => File => B] {
+    def apply(a: A)(pos: Position): B
+    def apply(a: Parsley[File => A]): Parsley[File => B] = error(ap1(pos.map(con), a))
+
+    override final def con(pos: (Int, Int)): (File => A) => File => B =
+      a => file => this.apply(a(file))(Position(pos._1, pos._2, file))
+  }
+
+  trait ParserBridgePos2Chain[-A, -B, +C]
+      extends ParserSingletonBridgePos[(File => A) => (File => B) => File => C] {
     def apply(a: A, b: B)(pos: Position): C
-    def apply(a: Parsley[A], b: => Parsley[B]): Parsley[C] = error(
+    def apply(a: Parsley[File => A]): Parsley[(File => B) => File => C] = error(
+      ap1(pos.map(con), a)
+    )
+
+    override final def con(pos: (Int, Int)): (File => A) => (File => B) => File => C =
+      a => b => file => this.apply(a(file), b(file))(Position(pos._1, pos._2, file))
+  }
+
+  trait ParserBridgePos2[-A, -B, +C]
+      extends ParserSingletonBridgePos[(File => A, File => B) => File => C] {
+    def apply(a: A, b: B)(pos: Position): C
+    def apply(a: Parsley[File => A], b: => Parsley[File => B]): Parsley[File => C] = error(
       ap2(pos.map(con), a, b)
     )
 
-    override final def con(pos: (Int, Int)): (A, B) => C =
-      apply(_, _)(Position(pos._1, pos._2))
+    override final def con(pos: (Int, Int)): (File => A, File => B) => File => C =
+      (a, b) => file => this.apply(a(file), b(file))(Position(pos._1, pos._2, file))
   }
 
-  trait ParserBridgePos3[-A, -B, -C, +D] extends ParserSingletonBridgePos[(A, B, C) => D] {
+  trait ParserBridgePos3[-A, -B, -C, +D]
+      extends ParserSingletonBridgePos[(File => A, File => B, File => C) => File => D] {
     def apply(a: A, b: B, c: C)(pos: Position): D
-    def apply(a: Parsley[A], b: => Parsley[B], c: => Parsley[C]): Parsley[D] = error(
+    def apply(
+        a: Parsley[File => A],
+        b: => Parsley[File => B],
+        c: => Parsley[File => C]
+    ): Parsley[File => D] = error(
       ap3(pos.map(con), a, b, c)
     )
 
-    override final def con(pos: (Int, Int)): (A, B, C) => D =
-      apply(_, _, _)(Position(pos._1, pos._2))
+    override final def con(pos: (Int, Int)): (File => A, File => B, File => C) => File => D =
+      (a, b, c) => file => apply(a(file), b(file), c(file))(Position(pos._1, pos._2, file))
   }
 }

src/main/wacc/frontend/lexer.scala

@@ -39,6 +39,17 @@ val errConfig = new ErrorConfig {
   )
 }
 object lexer {
+  val escapedChars: Map[String, Int] = Map(
+    "0" -> '\u0000',
+    "b" -> '\b',
+    "t" -> '\t',
+    "n" -> '\n',
+    "f" -> '\f',
+    "r" -> '\r',
+    "\\" -> '\\',
+    "'" -> '\'',
+    "\"" -> '\"'
+  )
 
   /** Language description for the WACC lexer
     */
@@ -63,15 +74,9 @@ object lexer {
     textDesc = TextDesc.plain.copy(
       graphicCharacter = Basic(c => c >= ' ' && c != '\\' && c != '\'' && c != '"'),
       escapeSequences = EscapeDesc.plain.copy(
-        literals = Set('\\', '"', '\''),
-        mapping = Map(
-          "0" -> '\u0000',
-          "b" -> '\b',
-          "t" -> '\t',
-          "n" -> '\n',
-          "f" -> '\f',
-          "r" -> '\r'
-        )
+        literals =
+          escapedChars.filter { (s, chr) => chr.toChar.toString == s }.map(_._2.toChar).toSet,
+        mapping = escapedChars.filter { (s, chr) => chr.toChar.toString != s }
       )
     ),
     numericDesc = NumericDesc.plain.copy(

src/main/wacc/frontend/microWacc.scala

@@ -0,0 +1,97 @@
+package wacc
+
+import cats.data.Chain
+
+object microWacc {
+  import wacc.ast.Position
+  import wacc.types._
+
+  sealed trait CallTarget(val retTy: SemType)
+  sealed trait Expr(val ty: SemType)
+  sealed trait LValue extends Expr
+
+  // Atomic expressions
+  case class IntLiter(v: Int) extends Expr(KnownType.Int)
+  case class BoolLiter(v: Boolean) extends Expr(KnownType.Bool)
+  case class CharLiter(v: Char) extends Expr(KnownType.Char)
+  case class ArrayLiter(elems: List[Expr])(ty: SemType, val pos: Position) extends Expr(ty)
+  case class NullLiter()(ty: SemType) extends Expr(ty)
+  case class Ident(name: String, uid: Int)(identTy: SemType)
+      extends Expr(identTy)
+      with CallTarget(identTy)
+      with LValue
+  case class ArrayElem(value: LValue, index: Expr)(ty: SemType) extends Expr(ty) with LValue
+
+  // Operators
+  case class UnaryOp(x: Expr, op: UnaryOperator)(ty: SemType) extends Expr(ty)
+  enum UnaryOperator {
+    case Negate
+    case Not
+    case Len
+    case Ord
+    case Chr
+  }
+  case class BinaryOp(x: Expr, y: Expr, op: BinaryOperator)(ty: SemType) extends Expr(ty)
+  enum BinaryOperator {
+    case Add
+    case Sub
+    case Mul
+    case Div
+    case Mod
+    case Greater
+    case GreaterEq
+    case Less
+    case LessEq
+    case Eq
+    case Neq
+    case And
+    case Or
+  }
+  object BinaryOperator {
+    def fromAst(op: ast.BinaryOp): BinaryOperator = op match {
+      case _: ast.Add       => Add
+      case _: ast.Sub       => Sub
+      case _: ast.Mul       => Mul
+      case _: ast.Div       => Div
+      case _: ast.Mod       => Mod
+      case _: ast.Greater   => Greater
+      case _: ast.GreaterEq => GreaterEq
+      case _: ast.Less      => Less
+      case _: ast.LessEq    => LessEq
+      case _: ast.Eq        => Eq
+      case _: ast.Neq       => Neq
+      case _: ast.And       => And
+      case _: ast.Or        => Or
+    }
+  }
+
+  // Statements
+  sealed trait Stmt {
+    val pos: Position
+  }
+
+  case class Builtin(val name: String)(retTy: SemType) extends CallTarget(retTy) {
+    override def toString(): String = name
+  }
+  object Builtin {
+    object Read extends Builtin("read")(?)
+    object Printf extends Builtin("printf")(?)
+    object Exit extends Builtin("exit")(?)
+    object Free extends Builtin("free")(?)
+    object Malloc extends Builtin("malloc")(?)
+    object PrintCharArray extends Builtin("printCharArray")(?)
+  }
+
+  case class Assign(lhs: LValue, rhs: Expr)(val pos: Position) extends Stmt
+  case class If(cond: Expr, thenBranch: Chain[Stmt], elseBranch: Chain[Stmt])(val pos: Position)
+      extends Stmt
+  case class While(cond: Expr, body: Chain[Stmt])(val pos: Position) extends Stmt
+  case class Call(target: CallTarget, args: List[Expr])(val pos: Position)
+      extends Stmt
+      with Expr(target.retTy)
+  case class Return(expr: Expr)(val pos: Position) extends Stmt
+
+  // Program
+  case class FuncDecl(name: Ident, params: List[Ident], body: Chain[Stmt])(val pos: Position)
+  case class Program(funcs: Chain[FuncDecl], stmts: Chain[Stmt])(val pos: Position)
+}

src/main/wacc/frontend/parser.scala

@@ -1,18 +1,22 @@
 package wacc
 
+import java.io.File
 import parsley.Result
 import parsley.Parsley
 import parsley.Parsley.{atomic, many, notFollowedBy, pure, unit}
-import parsley.combinator.{countSome, sepBy}
+import parsley.combinator.{countSome, sepBy, option}
 import parsley.expr.{precedence, SOps, InfixL, InfixN, InfixR, Prefix, Atoms}
 import parsley.errors.combinator._
 import parsley.errors.patterns.VerifiedErrors
 import parsley.syntax.zipped._
-import parsley.cats.combinator.{some}
+import parsley.cats.combinator.{some, sepBy1}
+import cats.syntax.all._
 import cats.data.NonEmptyList
 import parsley.errors.DefaultErrorBuilder
 import parsley.errors.ErrorBuilder
 import parsley.errors.tokenextractors.LexToken
+import parsley.expr.GOps
+import cats.Functor
 
 object parser {
   import lexer.implicits.implicitSymbol
@@ -52,13 +56,24 @@ object parser {
   implicit val builder: ErrorBuilder[String] = new DefaultErrorBuilder with LexToken {
     def tokens = errTokens
   }
-  def parse(input: String): Result[String, Program] = parser.parse(input)
-  private val parser = lexer.fully(`<program>`)
+  def parse(input: String): Result[String, File => PartialProgram] = parser.parse(input)
+  private val parser = lexer.fully(`<partial-program>`)
+
+  private type FParsley[A] = Parsley[File => A]
+
+  private def fParsley[A](p: Parsley[A]): FParsley[A] =
+    p map { a => file => a }
+
+  private def fPair[A, B](p: Parsley[(File => A, File => B)]): FParsley[(A, B)] =
+    p map { case (a, b) => file => (a(file), b(file)) }
+
+  private def fMap[A, F[_]: Functor](p: Parsley[F[File => A]]): FParsley[F[A]] =
+    p map { funcs => file => funcs.map(_(file)) }
 
   // Expressions
-  private lazy val `<expr>`: Parsley[Expr] = precedence {
-    SOps(InfixR)(Or from "||") +:
-      SOps(InfixR)(And from "&&") +:
+  private lazy val `<expr>`: FParsley[Expr] = precedence {
+    GOps(InfixR)(Or from "||") +:
+      GOps(InfixR)(And from "&&") +:
       SOps(InfixN)(Eq from "==", Neq from "!=") +:
       SOps(InfixN)(
         Less from "<",
@@ -83,32 +98,33 @@ object parser {
   }
 
   // Atoms
-  private lazy val `<atom>`: Atoms[Expr6] = Atoms(
+  private lazy val `<atom>`: Atoms[File => Expr6] = Atoms(
     IntLiter(integer).label("integer literal"),
     BoolLiter(("true" as true) | ("false" as false)).label("boolean literal"),
     CharLiter(charLit).label("character literal"),
-    StrLiter(stringLit).label("string literal"),
+    `<str-liter>`.label("string literal"),
     PairLiter from "null",
     `<ident-or-array-elem>`,
     Parens("(" ~> `<expr>` <~ ")")
   )
-  private val `<ident>` =
+  private lazy val `<str-liter>` = StrLiter(stringLit)
+  private lazy val `<ident>` =
     Ident(ident) | some("*" | "&").verifiedExplain("pointer operators are not allowed")
   private lazy val `<ident-or-array-elem>` =
     (`<ident>` <~ ("(".verifiedExplain(
       "functions can only be called using 'call' keyword"
     ) | unit)) <**> (`<array-indices>` </> identity)
-  private val `<array-indices>` = ArrayElem(some("[" ~> `<expr>` <~ "]"))
+  private lazy val `<array-indices>` = ArrayElem(fMap(some("[" ~> `<expr>` <~ "]")))
 
   // Types
-  private lazy val `<type>`: Parsley[Type] =
+  private lazy val `<type>`: FParsley[Type] =
     (`<base-type>` | (`<pair-type>` ~> `<pair-elems-type>`)) <**> (`<array-type>` </> identity)
   private val `<base-type>` =
     (IntType from "int") | (BoolType from "bool") | (CharType from "char") | (StringType from "string")
   private lazy val `<array-type>` =
-    ArrayType(countSome("[" ~> "]"))
+    ArrayType(fParsley(countSome("[" ~> "]")))
   private val `<pair-type>` = "pair"
-  private val `<pair-elems-type>`: Parsley[PairType] = PairType(
+  private val `<pair-elems-type>`: FParsley[PairType] = PairType(
     "(" ~> `<pair-elem-type>` <~ ",",
     `<pair-elem-type>` <~ ")"
   )
@@ -116,7 +132,7 @@ object parser {
     (`<base-type>` <**> (`<array-type>` </> identity)) |
       ((UntypedPairType from `<pair-type>`) <**>
         ((`<pair-elems-type>` <**> `<array-type>`)
-          .map(arr => (_: UntypedPairType) => arr) </> identity))
+          .map(arr => (_: File => UntypedPairType) => arr) </> identity))
 
   /* Statements
     Atomic is used in two places here:
@@ -127,13 +143,30 @@ object parser {
         invalid syntax check, this only happens at most once per program so this is not a major
         concern.
    */
+  private lazy val `<partial-program>` = PartialProgram(
+    fMap(many(`<import>`)),
+    `<program>`
+  )
+  private lazy val `<import>` = Import(
+    "import" ~> `<import-filename>`,
+    "(" ~> fMap(sepBy1(`<imported-func>`, ",")) <~ ")"
+  )
+  private lazy val `<import-filename>` = `<str-liter>`.label("import file name")
+  private lazy val `<imported-func>` = ImportedFunc(
+    `<ident>`.label("imported function name"),
+    fMap(option("as" ~> `<ident>`)).label("imported function alias")
+  )
   private lazy val `<program>` = Program(
     "begin" ~> (
-      many(
-        atomic(
-          `<type>`.label("function declaration") <~> `<ident>` <~ "("
-        ) <**> `<partial-func-decl>`
-      ).label("function declaration") |
+      fMap(
+        many(
+          fPair(
+            atomic(
+              `<type>`.label("function declaration") <~> `<ident>` <~ "("
+            )
+          ) <**> `<partial-func-decl>`
+        ).label("function declaration")
+      ) |
         atomic(`<ident>` <~ "(").verifiedExplain("function declaration is missing return type")
     ),
     `<stmt>`.label(
@@ -142,17 +175,23 @@ object parser {
   )
   private lazy val `<partial-func-decl>` =
     FuncDecl(
-      sepBy(`<param>`, ",") <~ ")" <~ "is",
-      `<stmt>`.guardAgainst {
-        case stmts if !stmts.isReturning => Seq("all functions must end in a returning statement")
-      } <~ "end"
+      fPair(
+        (fMap(sepBy(`<param>`, ",")) <~ ")" <~ "is") <~>
+          (`<stmt>`.guardAgainst {
+            // TODO: passing in an arbitrary file works but is ugly
+            case stmts if !(stmts(File("."))).isReturning =>
+              Seq("all functions must end in a returning statement")
+          } <~ "end")
+      )
     )
   private lazy val `<param>` = Param(`<type>`, `<ident>`)
-  private lazy val `<stmt>`: Parsley[NonEmptyList[Stmt]] =
-    (
-      `<basic-stmt>`.label("main program body"),
-      (many(";" ~> `<basic-stmt>`.label("statement after ';'"))) </> Nil
-    ).zipped(NonEmptyList.apply)
+  private lazy val `<stmt>`: FParsley[NonEmptyList[Stmt]] =
+    fMap(
+      (
+        `<basic-stmt>`.label("main program body"),
+        (many(";" ~> `<basic-stmt>`.label("statement after ';'"))) </> Nil
+      ).zipped(NonEmptyList.apply)
+    )
 
   private lazy val `<basic-stmt>` =
     (Skip from "skip")
@@ -160,8 +199,8 @@ object parser {
       | Free("free" ~> `<expr>`.labelAndExplain(LabelType.Expr))
       | Return("return" ~> `<expr>`.labelAndExplain(LabelType.Expr))
       | Exit("exit" ~> `<expr>`.labelAndExplain(LabelType.Expr))
-      | Print("print" ~> `<expr>`.labelAndExplain(LabelType.Expr), pure(false))
-      | Print("println" ~> `<expr>`.labelAndExplain(LabelType.Expr), pure(true))
+      | Print("print" ~> `<expr>`.labelAndExplain(LabelType.Expr), fParsley(pure(false)))
+      | Print("println" ~> `<expr>`.labelAndExplain(LabelType.Expr), fParsley(pure(true)))
       | If(
         "if" ~> `<expr>`.labelWithType(LabelType.Expr) <~ "then",
         `<stmt>` <~ "else",
@@ -185,9 +224,9 @@ object parser {
       ("call" ~> `<ident>`).verifiedExplain(
         "function calls' results must be assigned to a variable"
       )
-  private lazy val `<lvalue>`: Parsley[LValue] =
+  private lazy val `<lvalue>`: FParsley[LValue] =
     `<pair-elem>` | `<ident-or-array-elem>`
-  private lazy val `<rvalue>`: Parsley[RValue] =
+  private lazy val `<rvalue>`: FParsley[RValue] =
     `<array-liter>` |
       NewPair(
         "newpair" ~> "(" ~> `<expr>` <~ ",",
@@ -196,13 +235,13 @@ object parser {
       `<pair-elem>` |
       Call(
         "call" ~> `<ident>` <~ "(",
-        sepBy(`<expr>`, ",") <~ ")"
+        fMap(sepBy(`<expr>`, ",")) <~ ")"
       ) | `<expr>`.labelWithType(LabelType.Expr)
   private lazy val `<pair-elem>` =
     Fst("fst" ~> `<lvalue>`.label("valid pair"))
       | Snd("snd" ~> `<lvalue>`.label("valid pair"))
   private lazy val `<array-liter>` = ArrayLiter(
-    "[" ~> sepBy(`<expr>`, ",") <~ "]"
+    "[" ~> fMap(sepBy(`<expr>`, ",")) <~ "]"
   )
 
   extension (stmts: NonEmptyList[Stmt]) {

src/main/wacc/frontend/renamer.scala

@@ -0,0 +1,368 @@
+package wacc
+
+import java.io.File
+import scala.collection.mutable
+import cats.effect.IO
+import cats.implicits._
+import cats.data.Chain
+import cats.data.NonEmptyList
+import parsley.{Failure, Success}
+
+object renamer {
+  import ast._
+  import types._
+
+  val MAIN = "$main"
+
+  enum IdentType {
+    case Func
+    case Var
+  }
+
+  case class ScopeKey(path: String, name: String, identType: IdentType)
+  case class ScopeValue(id: Ident, public: Boolean)
+
+  class Scope(
+      private val current: mutable.Map[ScopeKey, ScopeValue],
+      private val parent: Map[ScopeKey, ScopeValue],
+      guidStart: Int = 0,
+      val guidInc: Int = 1
+  ) {
+    private var guid = guidStart
+    private var immutable = false
+
+    private def nextGuid(): Int = {
+      val id = guid
+      guid += guidInc
+      id
+    }
+
+    private def verifyMutable(): Unit = {
+      if (immutable) throw new IllegalStateException("Cannot modify an immutable scope")
+    }
+
+    /** Create a new scope with the current scope as its parent.
+      *
+      * To be used for single-threaded applications.
+      *
+      * @return
+      *   A new scope with an empty current scope, and this scope flattened into the parent scope.
+      */
+    def withSubscope[T](f: Scope => T): T = {
+      val subscope =
+        Scope(mutable.Map.empty, Map.empty.withDefault(current.withDefault(parent)), guid, guidInc)
+      immutable = true
+      val result = f(subscope)
+      guid = subscope.guid // Sync GUID
+      immutable = false
+      result
+    }
+
+    /** Create new scopes with the current scope as its parent and GUID numbering adjusted
+      * correctly.
+      *
+      * This will permanently mark the current scope as immutable, for thread safety.
+      *
+      * To be used for multi-threaded applications.
+      *
+      * @return
+      *   New scopes with an empty current scope, and this scope flattened into the parent scope.
+      */
+    def subscopes(n: Int): Seq[Scope] = {
+      verifyMutable()
+      immutable = true
+      (0 until n).map { i =>
+        Scope(
+          mutable.Map.empty,
+          Map.empty.withDefault(current.withDefault(parent)),
+          guid + i * guidInc,
+          guidInc * n
+        )
+      }
+    }
+
+    /** Attempt to add a new identifier to the current scope. If the identifier already exists in
+      * the current scope, add an error to the error list.
+      *
+      * @param name
+      *   The name of the identifier.
+      * @return
+      *   An error, if one occurred.
+      */
+    def add(name: Ident, public: Boolean = false): Chain[Error] = {
+      verifyMutable()
+      val path = name.pos.file.getCanonicalPath
+      val identType = name.ty match {
+        case _: SemType  => IdentType.Var
+        case _: FuncType => IdentType.Func
+      }
+      val key = ScopeKey(path, name.v, identType)
+      current.get(key) match {
+        case Some(ScopeValue(Ident(_, id, _), _)) =>
+          name.guid = id
+          Chain.one(Error.DuplicateDeclaration(name))
+        case None =>
+          name.guid = nextGuid()
+          current(key) = ScopeValue(name, public)
+          Chain.empty
+      }
+    }
+
+    /** Attempt to add a new identifier as an alias to another to the existing scope.
+      *
+      * @param alias
+      *   The (new) alias identifier.
+      * @param orig
+      *   The (existing) original identifier.
+      *
+      * @return
+      *   An error, if one occurred.
+      */
+    def addAlias(alias: Ident, orig: ScopeValue, public: Boolean = false): Chain[Error] = {
+      verifyMutable()
+      val path = alias.pos.file.getCanonicalPath
+      val identType = alias.ty match {
+        case _: SemType  => IdentType.Var
+        case _: FuncType => IdentType.Func
+      }
+      val key = ScopeKey(path, alias.v, identType)
+      current.get(key) match {
+        case Some(ScopeValue(Ident(_, id, _), _)) =>
+          alias.guid = id
+          Chain.one(Error.DuplicateDeclaration(alias))
+        case None =>
+          alias.guid = nextGuid()
+          current(key) = ScopeValue(orig.id, public)
+          Chain.empty
+      }
+    }
+
+    def get(path: String, name: String, identType: IdentType): Option[ScopeValue] =
+      // Unfortunately map defaults only work with `.apply()`, which throws an error when the key is not found.
+      // Neither is there a way to check whether a default exists, so we have to use a try-catch.
+      try {
+        Some(current.withDefault(parent)(ScopeKey(path, name, identType)))
+      } catch {
+        case _: NoSuchElementException => None
+      }
+
+    def getVar(name: Ident): Option[Ident] =
+      get(name.pos.file.getCanonicalPath, name.v, IdentType.Var).map(_.id)
+    def getFunc(name: Ident): Option[Ident] =
+      get(name.pos.file.getCanonicalPath, name.v, IdentType.Func).map(_.id)
+  }
+
+  def prepareGlobalScope(
+      partialProg: PartialProgram
+  )(using scope: Scope): IO[(FuncDecl, Chain[FuncDecl], Chain[Error])] = {
+    def readImportFile(file: File): IO[String] =
+      IO.blocking(os.read(os.Path(file.getCanonicalPath)))
+
+    def prepareImport(contents: String, file: File)(using
+        scope: Scope
+    ): IO[(Chain[FuncDecl], Chain[Error])] = {
+      parser.parse(contents) match {
+        case Failure(msg) =>
+          IO.pure(Chain.empty, Chain.one(Error.SyntaxError(file, msg)))
+        case Success(fn) =>
+          val partialProg = fn(file)
+          for {
+            (main, chunks, errors) <- prepareGlobalScope(partialProg)
+          } yield (main +: chunks, errors)
+      }
+    }
+
+    def addImportsToScope(importFile: File, funcs: NonEmptyList[ImportedFunc])(using
+        scope: Scope
+    ): Chain[Error] =
+      funcs.foldMap { case ImportedFunc(srcName, aliasName) =>
+        scope.get(importFile.getCanonicalPath, srcName.v, IdentType.Func) match {
+          case Some(src) if src.public =>
+            aliasName.ty = src.id.ty
+            scope.addAlias(aliasName, src)
+          case _ =>
+            Chain.one(Error.UndefinedFunction(srcName))
+        }
+      }
+
+    val PartialProgram(imports, prog) = partialProg
+
+    // First prepare this file's functions...
+    val Program(funcs, main) = prog
+    val (funcChunks, funcErrors) = funcs.foldLeft((Chain.empty[FuncDecl], Chain.empty[Error])) {
+      case ((chunks, errors), func @ FuncDecl(retType, name, params, body)) =>
+        val paramTypes = params.map { param =>
+          val paramType = SemType(param.paramType)
+          param.name.ty = paramType
+          paramType
+        }
+        name.ty = FuncType(SemType(retType), paramTypes)
+        (chunks :+ func, errors ++ scope.add(name, public = true))
+    }
+    // ...and main body.
+    val mainBodyIdent = Ident(MAIN, ty = FuncType(?, Nil))(main.head.pos)
+    val mainBodyErrors = scope.add(mainBodyIdent, public = false)
+    val mainBodyChunk = FuncDecl(IntType()(prog.pos), mainBodyIdent, Nil, main)(prog.pos)
+
+    // Now handle imports
+    val file = prog.pos.file
+    val preparedImports = imports.foldLeftM[IO, (Chain[FuncDecl], Chain[Error])](
+      (Chain.empty[FuncDecl], Chain.empty[Error])
+    ) { case ((chunks, errors), Import(name, funcs)) =>
+      val importFile = File(file.getParent, name.v)
+      if (!importFile.exists()) {
+        IO.pure(
+          (
+            chunks,
+            errors :+ Error.SemanticError(
+              name.pos,
+              s"File not found: ${importFile.getCanonicalPath}"
+            )
+          )
+        )
+      } else if (!importFile.canRead()) {
+        IO.pure(
+          (
+            chunks,
+            errors :+ Error.SemanticError(
+              name.pos,
+              s"File not readable: ${importFile.getCanonicalPath}"
+            )
+          )
+        )
+      } else if (importFile.getCanonicalPath == file.getCanonicalPath) {
+        IO.pure(
+          (
+            chunks,
+            errors :+ Error.SemanticError(
+              name.pos,
+              s"Cannot import self: ${importFile.getCanonicalPath}"
+            )
+          )
+        )
+      } else if (scope.get(importFile.getCanonicalPath, MAIN, IdentType.Func).isDefined) {
+        IO.pure(chunks, errors ++ addImportsToScope(importFile, funcs))
+      } else {
+        for {
+          contents <- readImportFile(importFile)
+          (importChunks, importErrors) <- prepareImport(contents, importFile)
+          importAliasErrors = addImportsToScope(importFile, funcs)
+        } yield (chunks ++ importChunks, errors ++ importErrors)
+      }
+    }
+
+    for {
+      (importChunks, importErrors) <- preparedImports
+      allChunks = importChunks ++ funcChunks
+      allErrors = importErrors ++ funcErrors ++ mainBodyErrors
+    } yield (mainBodyChunk, allChunks, allErrors)
+  }
+
+  /** Check scoping of all variables and flatten a program. Also generates semantic types and parses
+    * any imported files.
+    *
+    * @param partialProg
+    *   AST of the program
+    * @return
+    *   (flattenedProg, errors)
+    */
+  def renameFunction(funcScopePair: (FuncDecl, Scope)): IO[Chain[Error]] = {
+    val (FuncDecl(_, _, params, body), subscope) = funcScopePair
+    val paramErrors = params.foldMap(param => subscope.add(param.name))
+    IO(subscope.withSubscope { s => body.foldMap(rename(s)) })
+      .map(bodyErrors => paramErrors ++ bodyErrors)
+  }
+
+  /** Check scoping of all identifies in a given AST node.
+    *
+    * @param scope
+    *   The current scope and flattened parent scope.
+    * @param node
+    *   The AST node.
+    */
+  private def rename(scope: Scope)(node: Ident | Stmt | LValue | RValue | Expr): Chain[Error] =
+    node match {
+      // These cases are more interes/globting because the involve making subscopes
+      // or modifying the current scope.
+      case VarDecl(synType, name, value) => {
+        // Order matters here. Variable isn't declared until after the value is evaluated.
+        val errors = rename(scope)(value)
+        // Attempt to add the new variable to the current scope.
+        name.ty = SemType(synType)
+        errors ++ scope.add(name)
+      }
+      case If(cond, thenStmt, elseStmt) => {
+        val condErrors = rename(scope)(cond)
+        // then and else both have their own scopes
+        val thenErrors = scope.withSubscope(s => thenStmt.foldMap(rename(s)))
+        val elseErrors = scope.withSubscope(s => elseStmt.foldMap(rename(s)))
+        condErrors ++ thenErrors ++ elseErrors
+      }
+      case While(cond, body) => {
+        val condErrors = rename(scope)(cond)
+        // while bodies have their own scopes
+        val bodyErrors = scope.withSubscope(s => body.foldMap(rename(s)))
+        condErrors ++ bodyErrors
+      }
+      // begin-end blocks have their own scopes
+      case Block(body) => scope.withSubscope(s => body.foldMap(rename(s)))
+
+      // These cases are simpler, mostly just recursive calls to rename()
+      case Assign(lhs, value) => {
+        // Variables may be reassigned with their value in the rhs, so order doesn't matter here.
+        rename(scope)(lhs) ++ rename(scope)(value)
+      }
+      case Read(lhs)      => rename(scope)(lhs)
+      case Free(expr)     => rename(scope)(expr)
+      case Return(expr)   => rename(scope)(expr)
+      case Exit(expr)     => rename(scope)(expr)
+      case Print(expr, _) => rename(scope)(expr)
+      case NewPair(fst, snd) => {
+        rename(scope)(fst) ++ rename(scope)(snd)
+      }
+      case Call(name, args) => {
+        val nameErrors = scope.getFunc(name) match {
+          case Some(Ident(realName, guid, ty)) =>
+            name.v = realName
+            name.ty = ty
+            name.guid = guid
+            Chain.empty
+          case None =>
+            name.ty = FuncType(?, args.map(_ => ?))
+            scope.add(name)
+            Chain.one(Error.UndefinedFunction(name))
+        }
+        val argsErrors = args.foldMap(rename(scope))
+        nameErrors ++ argsErrors
+      }
+      case Fst(elem)         => rename(scope)(elem)
+      case Snd(elem)         => rename(scope)(elem)
+      case ArrayLiter(elems) => elems.foldMap(rename(scope))
+      case ArrayElem(name, indices) => {
+        val nameErrors = rename(scope)(name)
+        val indicesErrors = indices.foldMap(rename(scope))
+        nameErrors ++ indicesErrors
+      }
+      case Parens(expr) => rename(scope)(expr)
+      case op: UnaryOp  => rename(scope)(op.x)
+      case op: BinaryOp => {
+        rename(scope)(op.x) ++ rename(scope)(op.y)
+      }
+      // Default to variables. Only `call` uses IdentType.Func.
+      case id: Ident => {
+        scope.getVar(id) match {
+          case Some(Ident(_, guid, ty)) =>
+            id.ty = ty
+            id.guid = guid
+            Chain.empty
+          case None =>
+            id.ty = ?
+            scope.add(id)
+            Chain.one(Error.UndeclaredVariable(id))
+        }
+      }
+      // These literals cannot contain identifies, exit immediately.
+      case IntLiter(_) | BoolLiter(_) | CharLiter(_) | StrLiter(_) | PairLiter() | Skip() =>
+        Chain.empty
+    }
+}

src/main/wacc/frontend/semantics.scala

@@ -0,0 +1,42 @@
+package wacc
+
+import scala.collection.mutable
+import cats.implicits._
+import cats.data.Chain
+import cats.effect.IO
+
+object semantics {
+  import renamer.{Scope, prepareGlobalScope, renameFunction}
+  import typeChecker.checkFuncDecl
+
+  private def checkFunc(
+      funcDecl: ast.FuncDecl,
+      scope: Scope
+  ): IO[(microWacc.FuncDecl, Chain[Error])] = {
+    for {
+      renamerErrors <- renameFunction(funcDecl, scope)
+      (microWaccFunc, typeErrors) = checkFuncDecl(funcDecl)
+    } yield (microWaccFunc, renamerErrors ++ typeErrors)
+  }
+
+  def check(partialProg: ast.PartialProgram): IO[(microWacc.Program, Chain[Error])] = {
+    given scope: Scope = Scope(mutable.Map.empty, Map.empty)
+
+    for {
+      (main, chunks, globalErrors) <- prepareGlobalScope(partialProg)
+      toRename = (main +: chunks).toList
+      res <- toRename
+        .zip(scope.subscopes(toRename.size))
+        .parTraverse(checkFunc)
+      (typedChunks, errors) = res.foldLeft((Chain.empty[microWacc.FuncDecl], Chain.empty[Error])) {
+        case ((acc, err), (funcDecl, errors)) =>
+          (acc :+ funcDecl, err ++ errors)
+      }
+      (typedMain, funcs) = typedChunks.uncons match {
+        case Some((head, tail)) => (head.body, tail)
+        case None               => (Chain.empty, Chain.empty)
+      }
+    } yield (microWacc.Program(funcs, typedMain)(main.pos), globalErrors ++ errors)
+  }
+
+}

src/main/wacc/frontend/typeChecker.scala

@@ -0,0 +1,492 @@
+package wacc
+
+import cats.syntax.all._
+import cats.data.NonEmptyList
+import cats.data.Chain
+
+object typeChecker {
+  import wacc.types._
+
+  private enum Constraint {
+    case Unconstrained
+    // Allows weakening in one direction
+    case Is(ty: SemType, msg: String)
+    // Allows weakening in both directions, useful for array literals
+    case IsSymmetricCompatible(ty: SemType, msg: String)
+    // Does not allow weakening
+    case IsUnweakenable(ty: SemType, msg: String)
+    case IsEither(ty1: SemType, ty2: SemType, msg: String)
+    case Never(msg: String)
+  }
+
+  extension (ty: SemType) {
+
+    /** Check if a type satisfies a constraint.
+      *
+      * @param constraint
+      *   Constraint to satisfy.
+      * @param pos
+      *   Position to pass to the error, if constraint was not satisfied.
+      * @return
+      *   The type if the constraint was satisfied, or ? if it was not.
+      */
+    private def satisfies(constraint: Constraint, pos: ast.Position): (SemType, Chain[Error]) =
+      (ty, constraint) match {
+        case (KnownType.Array(KnownType.Char), Constraint.Is(KnownType.String, _)) =>
+          (KnownType.String, Chain.empty)
+        case (
+              KnownType.String,
+              Constraint.IsSymmetricCompatible(KnownType.Array(KnownType.Char), _)
+            ) =>
+          (KnownType.String, Chain.empty)
+        case (ty, Constraint.IsSymmetricCompatible(ty2, msg)) =>
+          ty.satisfies(Constraint.Is(ty2, msg), pos)
+        // Change to IsUnweakenable to disallow recursive weakening
+        case (ty, Constraint.Is(ty2, msg)) => ty.satisfies(Constraint.IsUnweakenable(ty2, msg), pos)
+        case (ty, Constraint.Unconstrained) => (ty, Chain.empty)
+        case (ty, Constraint.Never(msg)) =>
+          (?, Chain.one(Error.SemanticError(pos, msg)))
+        case (ty, Constraint.IsEither(ty1, ty2, msg)) =>
+          (ty moreSpecific ty1).orElse(ty moreSpecific ty2).map((_, Chain.empty)).getOrElse {
+            (?, Chain.one(Error.TypeMismatch(pos, ty1, ty, msg)))
+          }
+        case (ty, Constraint.IsUnweakenable(ty2, msg)) =>
+          (ty moreSpecific ty2).map((_, Chain.empty)).getOrElse {
+            (?, Chain.one(Error.TypeMismatch(pos, ty2, ty, msg)))
+          }
+      }
+
+    /** Tries to merge two types, returning the more specific one if possible.
+      *
+      * @param ty2
+      *   The other type to merge with.
+      * @return
+      *   The more specific type if it could be determined, or None if the types are incompatible.
+      */
+    private infix def moreSpecific(ty2: SemType): Option[SemType] =
+      (ty, ty2) match {
+        case (ty, ?)                  => Some(ty)
+        case (?, ty)                  => Some(ty)
+        case (ty1, ty2) if ty1 == ty2 => Some(ty1)
+        case (KnownType.Array(inn1), KnownType.Array(inn2)) =>
+          (inn1 moreSpecific inn2).map(KnownType.Array(_))
+        case (KnownType.Pair(fst1, snd1), KnownType.Pair(fst2, snd2)) =>
+          (fst1 moreSpecific fst2, snd1 moreSpecific snd2).mapN(KnownType.Pair(_, _))
+        case _ => None
+      }
+  }
+
+  /** Type-check a function declaration.
+    *
+    * @param func
+    *   The AST of the function to type-check.
+    */
+  def checkFuncDecl(func: ast.FuncDecl): (microWacc.FuncDecl, Chain[Error]) = {
+    val ast.FuncDecl(_, name, params, stmts) = func
+    val FuncType(retType, paramTypes) = name.ty.asInstanceOf[FuncType]
+    val returnConstraint =
+      if func.name.v == renamer.MAIN then Constraint.Never("main body must not return")
+      else Constraint.Is(retType, s"function ${name.v} must return $retType")
+    val (body, bodyErrors) = stmts.foldMap(checkStmt(_, returnConstraint))
+    (
+      microWacc.FuncDecl(
+        microWacc.Ident(name.v, name.guid)(retType),
+        params.zip(paramTypes).map { case (ast.Param(_, ident), ty) =>
+          microWacc.Ident(ident.v, ident.guid)(ty)
+        },
+        body
+      )(func.pos),
+      bodyErrors
+    )
+  }
+
+  /** Type-check an AST statement node.
+    *
+    * @param stmt
+    *   The statement to type-check.
+    * @param returnConstraint
+    *   The constraint that any `return <expr>` statements must satisfy.
+    */
+  private def checkStmt(
+      stmt: ast.Stmt,
+      returnConstraint: Constraint
+  ): (Chain[microWacc.Stmt], Chain[Error]) = stmt match {
+    // Ignore the type of the variable, since it has been converted to a SemType by the renamer.
+    case ast.VarDecl(_, name, value) =>
+      val expectedTy = name.ty
+      val (typedValue, valueErrors) = checkValue(
+        value,
+        Constraint.Is(
+          expectedTy.asInstanceOf[SemType],
+          s"variable ${name.v} must be assigned a value of type $expectedTy"
+        )
+      )
+      (
+        Chain.one(
+          microWacc.Assign(
+            microWacc.Ident(name.v, name.guid)(expectedTy.asInstanceOf[SemType]),
+            typedValue
+          )(stmt.pos)
+        ),
+        valueErrors
+      )
+    case ast.Assign(lhs, rhs) =>
+      val (lhsTyped, lhsErrors) = checkLValue(lhs, Constraint.Unconstrained)
+      val (rhsTyped, rhsErrors) =
+        checkValue(rhs, Constraint.Is(lhsTyped.ty, s"assignment must have type ${lhsTyped.ty}"))
+      val unknownError = (lhsTyped.ty, rhsTyped.ty) match {
+        case (?, ?) =>
+          Chain.one(
+            Error.SemanticError(lhs.pos, "assignment with both sides of unknown type is illegal")
+          )
+        case _ => Chain.empty
+      }
+      (
+        Chain.one(microWacc.Assign(lhsTyped, rhsTyped)(stmt.pos)),
+        lhsErrors ++ rhsErrors ++ unknownError
+      )
+    case ast.Read(dest) =>
+      val (destTyped, destErrors) = checkLValue(dest, Constraint.Unconstrained)
+      val (destTy, destTyErrors) = destTyped.ty match {
+        case ? =>
+          (
+            ?,
+            Chain.one(
+              Error.SemanticError(dest.pos, "cannot read into a destination with an unknown type")
+            )
+          )
+        case destTy =>
+          destTy.satisfies(
+            Constraint.IsEither(
+              KnownType.Int,
+              KnownType.Char,
+              "read must be applied to an int or char"
+            ),
+            dest.pos
+          )
+      }
+      (
+        Chain.one(
+          microWacc.Assign(
+            destTyped,
+            microWacc.Call(
+              microWacc.Builtin.Read,
+              List(
+                destTy match {
+                  case KnownType.Int      => " %d".toMicroWaccCharArray(stmt.pos)
+                  case KnownType.Char | _ => " %c".toMicroWaccCharArray(stmt.pos)
+                },
+                destTyped
+              )
+            )(dest.pos)
+          )(stmt.pos)
+        ),
+        destErrors ++ destTyErrors
+      )
+    case ast.Free(lhs) =>
+      val (lhsTyped, lhsErrors) = checkValue(
+        lhs,
+        Constraint.IsEither(
+          KnownType.Array(?),
+          KnownType.Pair(?, ?),
+          "free must be applied to an array or pair"
+        )
+      )
+      (Chain.one(microWacc.Call(microWacc.Builtin.Free, List(lhsTyped))(stmt.pos)), lhsErrors)
+    case ast.Return(expr) =>
+      val (exprTyped, exprErrors) = checkValue(expr, returnConstraint)
+      (Chain.one(microWacc.Return(exprTyped)(stmt.pos)), exprErrors)
+    case ast.Exit(expr) =>
+      val (exprTyped, exprErrors) =
+        checkValue(expr, Constraint.Is(KnownType.Int, "exit value must be int"))
+      (Chain.one(microWacc.Call(microWacc.Builtin.Exit, List(exprTyped))(stmt.pos)), exprErrors)
+    case ast.Print(expr, newline) =>
+      // This constraint should never fail, the scope-checker should have caught it already
+      val (exprTyped, exprErrors) = checkValue(expr, Constraint.Unconstrained)
+      val exprFormat = exprTyped.ty match {
+        case KnownType.Bool | KnownType.String             => "%s"
+        case KnownType.Array(KnownType.Char)               => "%.*s"
+        case KnownType.Char                                => "%c"
+        case KnownType.Int                                 => "%d"
+        case KnownType.Pair(_, _) | KnownType.Array(_) | ? => "%p"
+      }
+      val printfCall = { (func: microWacc.Builtin, value: microWacc.Expr) =>
+        Chain.one(
+          microWacc.Call(
+            func,
+            List(
+              s"$exprFormat${if newline then "\n" else ""}".toMicroWaccCharArray(stmt.pos),
+              value
+            )
+          )(stmt.pos)
+        )
+      }
+      (
+        exprTyped.ty match {
+          case KnownType.Bool =>
+            Chain.one(
+              microWacc.If(
+                exprTyped,
+                printfCall(microWacc.Builtin.Printf, "true".toMicroWaccCharArray(stmt.pos)),
+                printfCall(microWacc.Builtin.Printf, "false".toMicroWaccCharArray(stmt.pos))
+              )(stmt.pos)
+            )
+          case KnownType.Array(KnownType.Char) =>
+            printfCall(microWacc.Builtin.PrintCharArray, exprTyped)
+          case _ => printfCall(microWacc.Builtin.Printf, exprTyped)
+        },
+        exprErrors
+      )
+    case ast.If(cond, thenStmt, elseStmt) =>
+      val (condTyped, condErrors) =
+        checkValue(cond, Constraint.Is(KnownType.Bool, "if condition must be a bool"))
+      val (thenStmtTyped, thenErrors) = thenStmt.foldMap(checkStmt(_, returnConstraint))
+      val (elseStmtTyped, elseErrors) = elseStmt.foldMap(checkStmt(_, returnConstraint))
+      (
+        Chain.one(microWacc.If(condTyped, thenStmtTyped, elseStmtTyped)(cond.pos)),
+        condErrors ++ thenErrors ++ elseErrors
+      )
+    case ast.While(cond, body) =>
+      val (condTyped, condErrors) =
+        checkValue(cond, Constraint.Is(KnownType.Bool, "while condition must be a bool"))
+      val (bodyTyped, bodyErrors) = body.foldMap(checkStmt(_, returnConstraint))
+      (Chain.one(microWacc.While(condTyped, bodyTyped)(cond.pos)), condErrors ++ bodyErrors)
+    case ast.Block(body)   => body.foldMap(checkStmt(_, returnConstraint))
+    case skip @ ast.Skip() => (Chain.empty, Chain.empty)
+  }
+
+  /** Type-check an AST LValue, RValue or Expr node. This function does all 3 since these traits
+    * overlap in the AST.
+    *
+    * @param value
+    *   The value to type-check.
+    * @param constraint
+    *   The type constraint that the value must satisfy.
+    * @return
+    *   The most specific type of the value if it could be determined, or ? if it could not.
+    */
+  private def checkValue(
+      value: ast.LValue | ast.RValue | ast.Expr,
+      constraint: Constraint
+  ): (microWacc.Expr, Chain[Error]) = value match {
+    case l @ ast.IntLiter(v) =>
+      val (_, errors) = KnownType.Int.satisfies(constraint, l.pos)
+      (microWacc.IntLiter(v), errors)
+    case l @ ast.BoolLiter(v) =>
+      val (_, errors) = KnownType.Bool.satisfies(constraint, l.pos)
+      (microWacc.BoolLiter(v), errors)
+    case l @ ast.CharLiter(v) =>
+      val (_, errors) = KnownType.Char.satisfies(constraint, l.pos)
+      (microWacc.CharLiter(v), errors)
+    case l @ ast.StrLiter(v) =>
+      val (_, errors) = KnownType.String.satisfies(constraint, l.pos)
+      (v.toMicroWaccCharArray(l.pos), errors)
+    case l @ ast.PairLiter() =>
+      val (ty, errors) = KnownType.Pair(?, ?).satisfies(constraint, l.pos)
+      (microWacc.NullLiter()(ty), errors)
+    case ast.Parens(expr) => checkValue(expr, constraint)
+    case l @ ast.ArrayLiter(elems) =>
+      val ((elemTy, elemsErrors), elemsTyped) =
+        elems.mapAccumulate[(SemType, Chain[Error]), microWacc.Expr]((?, Chain.empty)) {
+          case ((acc, errors), elem) =>
+            val (elemTyped, elemErrors) = checkValue(
+              elem,
+              Constraint.IsSymmetricCompatible(acc, s"array elements must have the same type")
+            )
+            ((elemTyped.ty, errors ++ elemErrors), elemTyped)
+        }
+      val (arrayTy, arrayErrors) = KnownType
+        // Start with an unknown param type, make it more specific while checking the elements.
+        .Array(elemTy)
+        .satisfies(constraint, l.pos)
+      (microWacc.ArrayLiter(elemsTyped)(arrayTy, l.pos), elemsErrors ++ arrayErrors)
+    case l @ ast.NewPair(fst, snd) =>
+      val (fstTyped, fstErrors) = checkValue(fst, Constraint.Unconstrained)
+      val (sndTyped, sndErrors) = checkValue(snd, Constraint.Unconstrained)
+      val (pairTy, pairErrors) =
+        KnownType.Pair(fstTyped.ty, sndTyped.ty).satisfies(constraint, l.pos)
+      (
+        microWacc.ArrayLiter(List(fstTyped, sndTyped))(pairTy, l.pos),
+        fstErrors ++ sndErrors ++ pairErrors
+      )
+    case ast.Call(id, args) =>
+      val funcTy @ FuncType(retTy, paramTys) = id.ty.asInstanceOf[FuncType]
+      val lenError =
+        if (args.length == paramTys.length) then Chain.empty
+        else Chain.one(Error.FunctionParamsMismatch(id, paramTys.length, args.length, funcTy))
+      // Even if the number of arguments is wrong, we still check the types of the arguments
+      // in the best way we can (by taking a zip).
+      val (argsErrors, argsTyped) =
+        args.zip(paramTys).mapAccumulate(Chain.empty[Error]) { case (errors, (arg, paramTy)) =>
+          val (argTyped, argErrors) =
+            checkValue(arg, Constraint.Is(paramTy, s"argument type mismatch in function ${id.v}"))
+          (errors ++ argErrors, argTyped)
+        }
+      val (retTyChecked, retErrors) = retTy.satisfies(constraint, id.pos)
+      (
+        microWacc.Call(microWacc.Ident(id.v, id.guid)(retTyChecked), argsTyped)(id.pos),
+        lenError ++ argsErrors ++ retErrors
+      )
+
+    // Unary operators
+    case ast.Negate(x) =>
+      val (argTyped, argErrors) =
+        checkValue(x, Constraint.Is(KnownType.Int, "negation must be applied to an int"))
+      val (retTy, retErrors) = KnownType.Int.satisfies(constraint, x.pos)
+      (microWacc.UnaryOp(argTyped, microWacc.UnaryOperator.Negate)(retTy), argErrors ++ retErrors)
+    case ast.Not(x) =>
+      val (argTyped, argErrors) =
+        checkValue(x, Constraint.Is(KnownType.Bool, "logical not must be applied to a bool"))
+      val (retTy, retErrors) = KnownType.Bool.satisfies(constraint, x.pos)
+      (microWacc.UnaryOp(argTyped, microWacc.UnaryOperator.Not)(retTy), argErrors ++ retErrors)
+    case ast.Len(x) =>
+      val (argTyped, argErrors) =
+        checkValue(x, Constraint.Is(KnownType.Array(?), "len must be applied to an array"))
+      val (retTy, retErrors) = KnownType.Int.satisfies(constraint, x.pos)
+      (microWacc.UnaryOp(argTyped, microWacc.UnaryOperator.Len)(retTy), argErrors ++ retErrors)
+    case ast.Ord(x) =>
+      val (argTyped, argErrors) =
+        checkValue(x, Constraint.Is(KnownType.Char, "ord must be applied to a char"))
+      val (retTy, retErrors) = KnownType.Int.satisfies(constraint, x.pos)
+      (microWacc.UnaryOp(argTyped, microWacc.UnaryOperator.Ord)(retTy), argErrors ++ retErrors)
+    case ast.Chr(x) =>
+      val (argTyped, argErrors) =
+        checkValue(x, Constraint.Is(KnownType.Int, "chr must be applied to an int"))
+      val (retTy, retErrors) = KnownType.Char.satisfies(constraint, x.pos)
+      (microWacc.UnaryOp(argTyped, microWacc.UnaryOperator.Chr)(retTy), argErrors ++ retErrors)
+
+    // Binary operators
+    case op: (ast.Add | ast.Sub | ast.Mul | ast.Div | ast.Mod) =>
+      val operand = Constraint.Is(KnownType.Int, s"${op.name} operator must be applied to an int")
+      val (xTyped, xErrors) = checkValue(op.x, operand)
+      val (yTyped, yErrors) = checkValue(op.y, operand)
+      val (retTy, retErrors) = KnownType.Int.satisfies(constraint, op.pos)
+      (
+        microWacc.BinaryOp(xTyped, yTyped, microWacc.BinaryOperator.fromAst(op))(retTy),
+        xErrors ++ yErrors ++ retErrors
+      )
+    case op: (ast.Eq | ast.Neq) =>
+      val (xTyped, xErrors) = checkValue(op.x, Constraint.Unconstrained)
+      val (yTyped, yErrors) = checkValue(
+        op.y,
+        Constraint.Is(xTyped.ty, s"${op.name} operator must be applied to values of the same type")
+      )
+      val (retTy, retErrors) = KnownType.Bool.satisfies(constraint, op.pos)
+      (
+        microWacc.BinaryOp(xTyped, yTyped, microWacc.BinaryOperator.fromAst(op))(retTy),
+        xErrors ++ yErrors ++ retErrors
+      )
+    case op: (ast.Less | ast.LessEq | ast.Greater | ast.GreaterEq) =>
+      val xConstraint = Constraint.IsEither(
+        KnownType.Int,
+        KnownType.Char,
+        s"${op.name} operator must be applied to an int or char"
+      )
+      val (xTyped, xErrors) = checkValue(op.x, xConstraint)
+      // If x type-check failed, we still want to check y is an Int or Char (rather than ?)
+      val yConstraint = xTyped.ty match {
+        case ? => xConstraint
+        case xTy =>
+          Constraint.Is(xTy, s"${op.name} operator must be applied to values of the same type")
+      }
+      val (yTyped, yErrors) = checkValue(op.y, yConstraint)
+      val (retTy, retErrors) = KnownType.Bool.satisfies(constraint, op.pos)
+      (
+        microWacc.BinaryOp(xTyped, yTyped, microWacc.BinaryOperator.fromAst(op))(retTy),
+        xErrors ++ yErrors ++ retErrors
+      )
+    case op: (ast.And | ast.Or) =>
+      val operand = Constraint.Is(KnownType.Bool, s"${op.name} operator must be applied to a bool")
+      val (xTyped, xErrors) = checkValue(op.x, operand)
+      val (yTyped, yErrors) = checkValue(op.y, operand)
+      val (retTy, retErrors) = KnownType.Bool.satisfies(constraint, op.pos)
+      (
+        microWacc.BinaryOp(xTyped, yTyped, microWacc.BinaryOperator.fromAst(op))(retTy),
+        xErrors ++ yErrors ++ retErrors
+      )
+
+    case lvalue: ast.LValue => checkLValue(lvalue, constraint)
+  }
+
+  /** Type-check an AST LValue node. Separate because microWacc keeps LValues
+    *
+    * @param value
+    *   The value to type-check.
+    * @param constraint
+    *   The type constraint that the value must satisfy.
+    * @param ctx
+    *   The type checker context which includes the global names and functions, and an errors
+    *   builder.
+    * @return
+    *   The most specific type of the value if it could be determined, or ? if it could not.
+    */
+  private def checkLValue(
+      value: ast.LValue,
+      constraint: Constraint
+  ): (microWacc.LValue, Chain[Error]) = value match {
+    case id @ ast.Ident(name, guid, ty) =>
+      val (idTy, idErrors) = ty.asInstanceOf[SemType].satisfies(constraint, id.pos)
+      (microWacc.Ident(name, guid)(idTy), idErrors)
+    case ast.ArrayElem(id, indices) =>
+      val arrayTy = id.ty.asInstanceOf[SemType]
+      val ((elemTy, elemErrors), indicesTyped) =
+        indices.mapAccumulate((arrayTy.asInstanceOf[SemType], Chain.empty[Error])) {
+          case ((acc, errors), elem) =>
+            val (idxTyped, idxErrors) =
+              checkValue(elem, Constraint.Is(KnownType.Int, "array index must be an int"))
+            val (next, nextError) = acc match {
+              case KnownType.Array(innerTy) => (innerTy, Chain.empty)
+              case ? => (?, Chain.empty) // we can keep indexing an unknown type
+              case nonArrayTy =>
+                (
+                  ?,
+                  Chain.one(
+                    Error.TypeMismatch(
+                      elem.pos,
+                      KnownType.Array(?),
+                      acc,
+                      "cannot index into a non-array"
+                    )
+                  )
+                )
+            }
+            ((next, errors ++ idxErrors ++ nextError), idxTyped)
+        }
+      val (retTy, retErrors) = elemTy.satisfies(constraint, value.pos)
+      val firstArrayElem = microWacc.ArrayElem(
+        microWacc.Ident(id.v, id.guid)(arrayTy),
+        indicesTyped.head
+      )(retTy)
+      val arrayElem = indicesTyped.tail.foldLeft(firstArrayElem) { (acc, idx) =>
+        microWacc.ArrayElem(acc, idx)(KnownType.Array(acc.ty))
+      }
+      // Need to type-check the final arrayElem with the constraint
+      // TODO: What
+      (microWacc.ArrayElem(arrayElem.value, arrayElem.index)(retTy), elemErrors ++ retErrors)
+    case ast.Fst(elem) =>
+      val (elemTyped, elemErrors) = checkLValue(
+        elem,
+        Constraint.Is(KnownType.Pair(?, ?), "fst must be applied to a pair")
+      )
+      val (retTy, retErrors) = elemTyped.ty match {
+        case KnownType.Pair(left, _) => left.satisfies(constraint, elem.pos)
+        case _ => (?, Chain.one(Error.InternalError(elem.pos, "fst must be applied to a pair")))
+      }
+      (microWacc.ArrayElem(elemTyped, microWacc.IntLiter(0))(retTy), elemErrors ++ retErrors)
+    case ast.Snd(elem) =>
+      val (elemTyped, elemErrors) = checkLValue(
+        elem,
+        Constraint.Is(KnownType.Pair(?, ?), "snd must be applied to a pair")
+      )
+      val (retTy, retErrors) = elemTyped.ty match {
+        case KnownType.Pair(_, right) => right.satisfies(constraint, elem.pos)
+        case _ => (?, Chain.one(Error.InternalError(elem.pos, "snd must be applied to a pair")))
+      }
+      (microWacc.ArrayElem(elemTyped, microWacc.IntLiter(1))(retTy), elemErrors ++ retErrors)
+  }
+
+  extension (s: String) {
+    def toMicroWaccCharArray(pos: ast.Position): microWacc.ArrayLiter =
+      microWacc.ArrayLiter(s.map(microWacc.CharLiter(_)).toList)(KnownType.String, pos)
+  }
+}

src/main/wacc/frontend/types.scala

@@ -3,7 +3,9 @@ package wacc
 object types {
   import ast._
 
-  sealed trait SemType {
+  sealed trait RenamerType
+
+  sealed trait SemType extends RenamerType {
     override def toString(): String = this match {
       case KnownType.Int               => "int"
       case KnownType.Bool              => "bool"
@@ -41,5 +43,5 @@ object types {
     }
   }
 
-  case class FuncType(returnType: SemType, params: List[SemType])
+  case class FuncType(returnType: SemType, params: List[SemType]) extends RenamerType
 }

src/main/wacc/renamer.scala

@@ -1,219 +0,0 @@
-package wacc
-
-import scala.collection.mutable
-
-object renamer {
-  import ast._
-  import types._
-
-  private enum IdentType {
-    case Func
-    case Var
-  }
-
-  private class Scope(
-      val current: mutable.Map[(String, IdentType), Ident],
-      val parent: Map[(String, IdentType), Ident]
-  ) {
-
-    /** Create a new scope with the current scope as its parent.
-      *
-      * @return
-      *   A new scope with an empty current scope, and this scope flattened into the parent scope.
-      */
-    def subscope: Scope =
-      Scope(mutable.Map.empty, Map.empty.withDefault(current.withDefault(parent)))
-
-    /** Attempt to add a new identifier to the current scope. If the identifier already exists in
-      * the current scope, add an error to the error list.
-      *
-      * @param ty
-      *   The semantic type of the variable identifier, or function identifier type.
-      * @param name
-      *   The name of the identifier.
-      * @param globalNames
-      *   The global map of identifiers to semantic types - the identifier will be added to this
-      *   map.
-      * @param globalNumbering
-      *   The global map of identifier names to the number of times they have been declared - will
-      *   used to rename this identifier, and will be incremented.
-      * @param errors
-      *   The list of errors to append to.
-      */
-    def add(ty: SemType | FuncType, name: Ident)(using
-        globalNames: mutable.Map[Ident, SemType],
-        globalFuncs: mutable.Map[Ident, FuncType],
-        globalNumbering: mutable.Map[String, Int],
-        errors: mutable.Builder[Error, List[Error]]
-    ) = {
-      val identType = ty match {
-        case _: SemType  => IdentType.Var
-        case _: FuncType => IdentType.Func
-      }
-      current.get((name.v, identType)) match {
-        case Some(Ident(_, uid)) =>
-          errors += Error.DuplicateDeclaration(name)
-          name.uid = uid
-        case None =>
-          val uid = globalNumbering.getOrElse(name.v, 0)
-          name.uid = uid
-          current((name.v, identType)) = name
-
-          ty match {
-            case semType: SemType =>
-              globalNames(name) = semType
-            case funcType: FuncType =>
-              globalFuncs(name) = funcType
-          }
-          globalNumbering(name.v) = uid + 1
-      }
-    }
-
-    private def get(name: String, identType: IdentType): Option[Ident] =
-      // Unfortunately map defaults only work with `.apply()`, which throws an error when the key is not found.
-      // Neither is there a way to check whether a default exists, so we have to use a try-catch.
-      try {
-        Some(current.withDefault(parent)((name, identType)))
-      } catch {
-        case _: NoSuchElementException => None
-      }
-
-    def getVar(name: String): Option[Ident] = get(name, IdentType.Var)
-    def getFunc(name: String): Option[Ident] = get(name, IdentType.Func)
-  }
-
-  /** Check scoping of all variables and functions in the program. Also generate semantic types for
-    * all identifiers.
-    *
-    * @param prog
-    *   AST of the program
-    * @param errors
-    *   List of errors to append to
-    * @return
-    *   Map of all (renamed) identifies to their semantic types
-    */
-  def rename(prog: Program)(using
-      errors: mutable.Builder[Error, List[Error]]
-  ): (Map[Ident, SemType], Map[Ident, FuncType]) = {
-    given globalNames: mutable.Map[Ident, SemType] = mutable.Map.empty
-    given globalFuncs: mutable.Map[Ident, FuncType] = mutable.Map.empty
-    given globalNumbering: mutable.Map[String, Int] = mutable.Map.empty
-    val scope = Scope(mutable.Map.empty, Map.empty)
-    val Program(funcs, main) = prog
-    funcs
-      // First add all function declarations to the scope
-      .map { case FuncDecl(retType, name, params, body) =>
-        val paramTypes = params.map { param =>
-          val paramType = SemType(param.paramType)
-          paramType
-        }
-        scope.add(FuncType(SemType(retType), paramTypes), name)
-        (params zip paramTypes, body)
-      }
-      // Only then rename the function bodies
-      // (functions can call one-another regardless of order of declaration)
-      .foreach { case (params, body) =>
-        val functionScope = scope.subscope
-        params.foreach { case (param, paramType) =>
-          functionScope.add(paramType, param.name)
-        }
-        body.toList.foreach(rename(functionScope.subscope)) // body can shadow function params
-      }
-    main.toList.foreach(rename(scope))
-    (globalNames.toMap, globalFuncs.toMap)
-  }
-
-  /** Check scoping of all identifies in a given AST node.
-    *
-    * @param scope
-    *   The current scope and flattened parent scope.
-    * @param node
-    *   The AST node.
-    * @param globalNames
-    *   The global map of identifiers to semantic types - renamed identifiers will be added to this
-    *   map.
-    * @param globalNumbering
-    *   The global map of identifier names to the number of times they have been declared - used and
-    *   updated during identifier renaming.
-    * @param errors
-    */
-  private def rename(scope: Scope)(
-      node: Ident | Stmt | LValue | RValue | Expr
-  )(using
-      globalNames: mutable.Map[Ident, SemType],
-      globalFuncs: mutable.Map[Ident, FuncType],
-      globalNumbering: mutable.Map[String, Int],
-      errors: mutable.Builder[Error, List[Error]]
-  ): Unit = node match {
-    // These cases are more interesting because the involve making subscopes
-    // or modifying the current scope.
-    case VarDecl(synType, name, value) => {
-      // Order matters here. Variable isn't declared until after the value is evaluated.
-      rename(scope)(value)
-      // Attempt to add the new variable to the current scope.
-      scope.add(SemType(synType), name)
-    }
-    case If(cond, thenStmt, elseStmt) => {
-      rename(scope)(cond)
-      // then and else both have their own scopes
-      thenStmt.toList.foreach(rename(scope.subscope))
-      elseStmt.toList.foreach(rename(scope.subscope))
-    }
-    case While(cond, body) => {
-      rename(scope)(cond)
-      // while bodies have their own scopes
-      body.toList.foreach(rename(scope.subscope))
-    }
-    // begin-end blocks have their own scopes
-    case Block(body) => body.toList.foreach(rename(scope.subscope))
-
-    // These cases are simpler, mostly just recursive calls to rename()
-    case Assign(lhs, value) => {
-      // Variables may be reassigned with their value in the rhs, so order doesn't matter here.
-      rename(scope)(lhs)
-      rename(scope)(value)
-    }
-    case Read(lhs)      => rename(scope)(lhs)
-    case Free(expr)     => rename(scope)(expr)
-    case Return(expr)   => rename(scope)(expr)
-    case Exit(expr)     => rename(scope)(expr)
-    case Print(expr, _) => rename(scope)(expr)
-    case NewPair(fst, snd) => {
-      rename(scope)(fst)
-      rename(scope)(snd)
-    }
-    case Call(name, args) => {
-      scope.getFunc(name.v) match {
-        case Some(Ident(_, uid)) => name.uid = uid
-        case None =>
-          errors += Error.UndefinedFunction(name)
-          scope.add(FuncType(?, args.map(_ => ?)), name)
-      }
-      args.foreach(rename(scope))
-    }
-    case Fst(elem)         => rename(scope)(elem)
-    case Snd(elem)         => rename(scope)(elem)
-    case ArrayLiter(elems) => elems.foreach(rename(scope))
-    case ArrayElem(name, indices) => {
-      rename(scope)(name)
-      indices.toList.foreach(rename(scope))
-    }
-    case Parens(expr) => rename(scope)(expr)
-    case op: UnaryOp  => rename(scope)(op.x)
-    case op: BinaryOp => {
-      rename(scope)(op.x)
-      rename(scope)(op.y)
-    }
-    // Default to variables. Only `call` uses IdentType.Func.
-    case id: Ident => {
-      scope.getVar(id.v) match {
-        case Some(Ident(_, uid)) => id.uid = uid
-        case None =>
-          errors += Error.UndeclaredVariable(id)
-          scope.add(?, id)
-      }
-    }
-    // These literals cannot contain identifies, exit immediately.
-    case IntLiter(_) | BoolLiter(_) | CharLiter(_) | StrLiter(_) | PairLiter() | Skip() => ()
-  }
-}

src/main/wacc/typeChecker.scala

@@ -1,322 +0,0 @@
-package wacc
-
-import cats.syntax.all._
-import scala.collection.mutable
-
-object typeChecker {
-  import wacc.ast._
-  import wacc.types._
-
-  case class TypeCheckerCtx(
-      globalNames: Map[Ident, SemType],
-      globalFuncs: Map[Ident, FuncType],
-      errors: mutable.Builder[Error, List[Error]]
-  ) {
-    def typeOf(ident: Ident): SemType = globalNames(ident)
-
-    def funcType(ident: Ident): FuncType = globalFuncs(ident)
-
-    def error(err: Error): SemType =
-      errors += err
-      ?
-  }
-
-  private enum Constraint {
-    case Unconstrained
-    // Allows weakening in one direction
-    case Is(ty: SemType, msg: String)
-    // Allows weakening in both directions, useful for array literals
-    case IsSymmetricCompatible(ty: SemType, msg: String)
-    // Does not allow weakening
-    case IsUnweakenable(ty: SemType, msg: String)
-    case IsEither(ty1: SemType, ty2: SemType, msg: String)
-    case Never(msg: String)
-  }
-
-  extension (ty: SemType) {
-
-    /** Check if a type satisfies a constraint.
-      *
-      * @param constraint
-      *   Constraint to satisfy.
-      * @param pos
-      *   Position to pass to the error, if constraint was not satisfied.
-      * @return
-      *   The type if the constraint was satisfied, or ? if it was not.
-      */
-    private def satisfies(constraint: Constraint, pos: Position)(using
-        ctx: TypeCheckerCtx
-    ): SemType =
-      (ty, constraint) match {
-        case (KnownType.Array(KnownType.Char), Constraint.Is(KnownType.String, _)) =>
-          KnownType.String
-        case (
-              KnownType.String,
-              Constraint.IsSymmetricCompatible(KnownType.Array(KnownType.Char), _)
-            ) =>
-          KnownType.String
-        case (ty, Constraint.IsSymmetricCompatible(ty2, msg)) =>
-          ty.satisfies(Constraint.Is(ty2, msg), pos)
-        // Change to IsUnweakenable to disallow recursive weakening
-        case (ty, Constraint.Is(ty2, msg)) => ty.satisfies(Constraint.IsUnweakenable(ty2, msg), pos)
-        case (ty, Constraint.Unconstrained) => ty
-        case (ty, Constraint.Never(msg)) =>
-          ctx.error(Error.SemanticError(pos, msg))
-        case (ty, Constraint.IsEither(ty1, ty2, msg)) =>
-          (ty moreSpecific ty1).orElse(ty moreSpecific ty2).getOrElse {
-            ctx.error(Error.TypeMismatch(pos, ty1, ty, msg))
-          }
-        case (ty, Constraint.IsUnweakenable(ty2, msg)) =>
-          (ty moreSpecific ty2).getOrElse {
-            ctx.error(Error.TypeMismatch(pos, ty2, ty, msg))
-          }
-      }
-
-    /** Tries to merge two types, returning the more specific one if possible.
-      *
-      * @param ty2
-      *   The other type to merge with.
-      * @return
-      *   The more specific type if it could be determined, or None if the types are incompatible.
-      */
-    private infix def moreSpecific(ty2: SemType): Option[SemType] =
-      (ty, ty2) match {
-        case (ty, ?)                  => Some(ty)
-        case (?, ty)                  => Some(ty)
-        case (ty1, ty2) if ty1 == ty2 => Some(ty1)
-        case (KnownType.Array(inn1), KnownType.Array(inn2)) =>
-          (inn1 moreSpecific inn2).map(KnownType.Array(_))
-        case (KnownType.Pair(fst1, snd1), KnownType.Pair(fst2, snd2)) =>
-          (fst1 moreSpecific fst2, snd1 moreSpecific snd2).mapN(KnownType.Pair(_, _))
-        case _ => None
-      }
-  }
-
-  /** Type-check a WACC program.
-    *
-    * @param prog
-    *   The AST of the program to type-check.
-    * @param ctx
-    *   The type checker context which includes the global names and functions, and an errors
-    *   builder.
-    */
-  def check(prog: Program)(using
-      ctx: TypeCheckerCtx
-  ): Unit = {
-    // Ignore function syntax types for return value and params, since those have been converted
-    // to SemTypes by the renamer.
-    prog.funcs.foreach { case FuncDecl(_, name, _, stmts) =>
-      val FuncType(retType, _) = ctx.funcType(name)
-      stmts.toList.foreach(
-        checkStmt(_, Constraint.Is(retType, s"function ${name.v} must return $retType"))
-      )
-    }
-    prog.main.toList.foreach(checkStmt(_, Constraint.Never("main function must not return")))
-  }
-
-  /** Type-check an AST statement node.
-    *
-    * @param stmt
-    *   The statement to type-check.
-    * @param returnConstraint
-    *   The constraint that any `return <expr>` statements must satisfy.
-    */
-  private def checkStmt(stmt: Stmt, returnConstraint: Constraint)(using
-      ctx: TypeCheckerCtx
-  ): Unit = stmt match {
-    // Ignore the type of the variable, since it has been converted to a SemType by the renamer.
-    case VarDecl(_, name, value) =>
-      val expectedTy = ctx.typeOf(name)
-      checkValue(
-        value,
-        Constraint.Is(
-          expectedTy,
-          s"variable ${name.v} must be assigned a value of type $expectedTy"
-        )
-      )
-    case Assign(lhs, rhs) =>
-      val lhsTy = checkValue(lhs, Constraint.Unconstrained)
-      (lhsTy, checkValue(rhs, Constraint.Is(lhsTy, s"assignment must have type $lhsTy"))) match {
-        case (?, ?) =>
-          ctx.error(
-            Error.SemanticError(lhs.pos, "assignment with both sides of unknown type is illegal")
-          )
-        case _ => ()
-      }
-    case Read(dest) =>
-      checkValue(dest, Constraint.Unconstrained) match {
-        case ? =>
-          ctx.error(
-            Error.SemanticError(dest.pos, "cannot read into a destination with an unknown type")
-          )
-        case destTy =>
-          destTy.satisfies(
-            Constraint.IsEither(
-              KnownType.Int,
-              KnownType.Char,
-              "read must be applied to an int or char"
-            ),
-            dest.pos
-          )
-      }
-    case Free(lhs) =>
-      checkValue(
-        lhs,
-        Constraint.IsEither(
-          KnownType.Array(?),
-          KnownType.Pair(?, ?),
-          "free must be applied to an array or pair"
-        )
-      )
-    case Return(expr) =>
-      checkValue(expr, returnConstraint)
-    case Exit(expr) =>
-      checkValue(expr, Constraint.Is(KnownType.Int, "exit value must be int"))
-    case Print(expr, _) =>
-      // This constraint should never fail, the scope-checker should have caught it already
-      checkValue(expr, Constraint.Unconstrained)
-    case If(cond, thenStmt, elseStmt) =>
-      checkValue(cond, Constraint.Is(KnownType.Bool, "if condition must be a bool"))
-      thenStmt.toList.foreach(checkStmt(_, returnConstraint))
-      elseStmt.toList.foreach(checkStmt(_, returnConstraint))
-    case While(cond, body) =>
-      checkValue(cond, Constraint.Is(KnownType.Bool, "while condition must be a bool"))
-      body.toList.foreach(checkStmt(_, returnConstraint))
-    case Block(body) =>
-      body.toList.foreach(checkStmt(_, returnConstraint))
-    case Skip() => ()
-  }
-
-  /** Type-check an AST LValue, RValue or Expr node. This function does all 3 since these traits
-    * overlap in the AST.
-    *
-    * @param value
-    *   The value to type-check.
-    * @param constraint
-    *   The type constraint that the value must satisfy.
-    * @return
-    *   The most specific type of the value if it could be determined, or ? if it could not.
-    */
-  private def checkValue(value: LValue | RValue | Expr, constraint: Constraint)(using
-      ctx: TypeCheckerCtx
-  ): SemType = value match {
-    case l @ IntLiter(_)  => KnownType.Int.satisfies(constraint, l.pos)
-    case l @ BoolLiter(_) => KnownType.Bool.satisfies(constraint, l.pos)
-    case l @ CharLiter(_) => KnownType.Char.satisfies(constraint, l.pos)
-    case l @ StrLiter(_)  => KnownType.String.satisfies(constraint, l.pos)
-    case l @ PairLiter()  => KnownType.Pair(?, ?).satisfies(constraint, l.pos)
-    case id: Ident =>
-      ctx.typeOf(id).satisfies(constraint, id.pos)
-    case ArrayElem(id, indices) =>
-      val arrayTy = ctx.typeOf(id)
-      val elemTy = indices.foldLeftM(arrayTy) { (acc, elem) =>
-        checkValue(elem, Constraint.Is(KnownType.Int, "array index must be an int"))
-        acc match {
-          case KnownType.Array(innerTy) => Some(innerTy)
-          case ?                        => Some(?) // we can keep indexing an unknown type
-          case nonArrayTy =>
-            ctx.error(
-              Error.TypeMismatch(elem.pos, KnownType.Array(?), acc, "cannot index into a non-array")
-            )
-            None
-        }
-      }
-      elemTy.getOrElse(?).satisfies(constraint, id.pos)
-    case Parens(expr) => checkValue(expr, constraint)
-    case l @ ArrayLiter(elems) =>
-      KnownType
-        // Start with an unknown param type, make it more specific while checking the elements.
-        .Array(elems.foldLeft[SemType](?) { case (acc, elem) =>
-          checkValue(
-            elem,
-            Constraint.IsSymmetricCompatible(acc, s"array elements must have the same type")
-          )
-        })
-        .satisfies(constraint, l.pos)
-    case l @ NewPair(fst, snd) =>
-      KnownType
-        .Pair(
-          checkValue(fst, Constraint.Unconstrained),
-          checkValue(snd, Constraint.Unconstrained)
-        )
-        .satisfies(constraint, l.pos)
-    case Call(id, args) =>
-      val funcTy @ FuncType(retTy, paramTys) = ctx.funcType(id)
-      if (args.length != paramTys.length) {
-        ctx.error(Error.FunctionParamsMismatch(id, paramTys.length, args.length, funcTy))
-      }
-      // Even if the number of arguments is wrong, we still check the types of the arguments
-      // in the best way we can (by taking a zip).
-      args.zip(paramTys).foreach { case (arg, paramTy) =>
-        checkValue(arg, Constraint.Is(paramTy, s"argument type mismatch in function ${id.v}"))
-      }
-      retTy.satisfies(constraint, id.pos)
-    case Fst(elem) =>
-      checkValue(
-        elem,
-        Constraint.Is(KnownType.Pair(?, ?), "fst must be applied to a pair")
-      ) match {
-        case what @ KnownType.Pair(left, _) =>
-          left.satisfies(constraint, elem.pos)
-        case _ => ctx.error(Error.InternalError(elem.pos, "fst must be applied to a pair"))
-      }
-    case Snd(elem) =>
-      checkValue(
-        elem,
-        Constraint.Is(KnownType.Pair(?, ?), "snd must be applied to a pair")
-      ) match {
-        case KnownType.Pair(_, right) => right.satisfies(constraint, elem.pos)
-        case _ => ctx.error(Error.InternalError(elem.pos, "snd must be applied to a pair"))
-      }
-
-    // Unary operators
-    case Negate(x) =>
-      checkValue(x, Constraint.Is(KnownType.Int, "negation must be applied to an int"))
-      KnownType.Int.satisfies(constraint, x.pos)
-    case Not(x) =>
-      checkValue(x, Constraint.Is(KnownType.Bool, "logical not must be applied to a bool"))
-      KnownType.Bool.satisfies(constraint, x.pos)
-    case Len(x) =>
-      checkValue(x, Constraint.Is(KnownType.Array(?), "len must be applied to an array"))
-      KnownType.Int.satisfies(constraint, x.pos)
-    case Ord(x) =>
-      checkValue(x, Constraint.Is(KnownType.Char, "ord must be applied to a char"))
-      KnownType.Int.satisfies(constraint, x.pos)
-    case Chr(x) =>
-      checkValue(x, Constraint.Is(KnownType.Int, "chr must be applied to an int"))
-      KnownType.Char.satisfies(constraint, x.pos)
-
-    // Binary operators
-    case op: (Add | Sub | Mul | Div | Mod) =>
-      val operand = Constraint.Is(KnownType.Int, s"${op.name} operator must be applied to an int")
-      checkValue(op.x, operand)
-      checkValue(op.y, operand)
-      KnownType.Int.satisfies(constraint, op.pos)
-    case op: (Eq | Neq) =>
-      val xTy = checkValue(op.x, Constraint.Unconstrained)
-      checkValue(
-        op.y,
-        Constraint.Is(xTy, s"${op.name} operator must be applied to values of the same type")
-      )
-      KnownType.Bool.satisfies(constraint, op.pos)
-    case op: (Less | LessEq | Greater | GreaterEq) =>
-      val xConstraint = Constraint.IsEither(
-        KnownType.Int,
-        KnownType.Char,
-        s"${op.name} operator must be applied to an int or char"
-      )
-      // If x type-check failed, we still want to check y is an Int or Char (rather than ?)
-      val yConstraint = checkValue(op.x, xConstraint) match {
-        case ? => xConstraint
-        case xTy =>
-          Constraint.Is(xTy, s"${op.name} operator must be applied to values of the same type")
-      }
-      checkValue(op.y, yConstraint)
-      KnownType.Bool.satisfies(constraint, op.pos)
-    case op: (And | Or) =>
-      val operand = Constraint.Is(KnownType.Bool, s"${op.name} operator must be applied to a bool")
-      checkValue(op.x, operand)
-      checkValue(op.y, operand)
-      KnownType.Bool.satisfies(constraint, op.pos)
-  }
-}

src/test/wacc/backend/extensionsSpec.scala

@@ -0,0 +1,66 @@
+package wacc
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.Inspectors.forEvery
+import cats.data.Chain
+
+class ExtensionsSpec extends AnyFlatSpec {
+  import asmGenerator.concatAll
+  import asmGenerator.escaped
+
+  behavior of "concatAll"
+
+  it should "handle int chains" in {
+    val chain = Chain(1, 2, 3).concatAll(
+      Chain(4, 5, 6),
+      Chain.empty,
+      Chain.one(-1)
+    )
+    assert(chain == Chain(1, 2, 3, 4, 5, 6, -1))
+  }
+
+  it should "handle AsmLine chains" in {
+    object lines {
+      import assemblyIR._
+      import assemblyIR.commonRegisters._
+      val main = LabelDef("main")
+      val pop = Pop(RAX)
+      val add = Add(RAX, ImmediateVal(1))
+      val push = Push(RAX)
+      val ret = Return()
+    }
+    val chain = Chain(lines.main).concatAll(
+      Chain.empty,
+      Chain.one(lines.pop),
+      Chain(lines.add, lines.push),
+      Chain.one(lines.ret)
+    )
+    assert(chain == Chain(lines.main, lines.pop, lines.add, lines.push, lines.ret))
+  }
+
+  behavior of "escaped"
+
+  val escapedStrings = Map(
+    "hello" -> "hello",
+    "world" -> "world",
+    "hello\nworld" -> "hello\\nworld",
+    "hello\tworld" -> "hello\\tworld",
+    "hello\\world" -> "hello\\\\world",
+    "hello\"world" -> "hello\\\"world",
+    "hello'world" -> "hello\\'world",
+    "hello\\nworld" -> "hello\\\\nworld",
+    "hello\\tworld" -> "hello\\\\tworld",
+    "hello\\\\world" -> "hello\\\\\\\\world",
+    "hello\\\"world" -> "hello\\\\\\\"world",
+    "hello\\'world" -> "hello\\\\\\'world",
+    "hello\\n\\t\\'world" -> "hello\\\\n\\\\t\\\\\\'world",
+    "hello\u0000world" -> "hello\\0world",
+    "hello\bworld" -> "hello\\bworld",
+    "hello\fworld" -> "hello\\fworld"
+  )
+  forEvery(escapedStrings) { (input, expected) =>
+    it should s"return $expected" in {
+      assert(input.escaped == expected)
+    }
+  }
+}

src/test/wacc/backend/instructionSpec.scala

@@ -0,0 +1,68 @@
+import org.scalatest.funsuite.AnyFunSuite
+import wacc.assemblyIR._
+import wacc.assemblyIR.Size._
+import wacc.assemblyIR.RegName._
+
+class instructionSpec extends AnyFunSuite {
+
+  val named64BitRegister = Register(Q64, AX)
+
+  test("named 64-bit register toString") {
+    assert(named64BitRegister.toString == "rax")
+  }
+
+  val named32BitRegister = Register(D32, AX)
+
+  test("named 32-bit register toString") {
+    assert(named32BitRegister.toString == "eax")
+  }
+
+  val scratch64BitRegister = Register(Q64, R8)
+
+  test("scratch 64-bit register toString") {
+    assert(scratch64BitRegister.toString == "r8")
+  }
+
+  val scratch32BitRegister = Register(D32, R8)
+
+  test("scratch 32-bit register toString") {
+    assert(scratch32BitRegister.toString == "r8d")
+  }
+
+  val memLocationWithRegister = MemLocation(named64BitRegister, opSize = Some(Q64))
+
+  test("mem location with register toString") {
+    assert(memLocationWithRegister.toString == "qword ptr [rax]")
+  }
+
+  val memLocationFull =
+    MemLocation(named64BitRegister, 32, (scratch64BitRegister, 10), Some(B8))
+
+  test("mem location with all fields toString") {
+    assert(memLocationFull.toString == "byte ptr [rax + r8 * 10 + 32]")
+  }
+
+  val immediateVal = ImmediateVal(123)
+
+  test("immediate value toString") {
+    assert(immediateVal.toString == "123")
+  }
+
+  val addInstruction = Add(named64BitRegister, immediateVal)
+
+  test("x86: add instruction toString") {
+    assert(addInstruction.toString == "\tadd rax, 123")
+  }
+
+  val subInstruction = Subtract(scratch64BitRegister, named64BitRegister)
+
+  test("x86: sub instruction toString") {
+    assert(subInstruction.toString == "\tsub r8, rax")
+  }
+
+  val callInstruction = Call(CLibFunc.Scanf)
+
+  test("x86: call instruction toString") {
+    assert(callInstruction.toString == "\tcall scanf@plt")
+  }
+}

src/test/wacc/backend/labelGeneratorSpec.scala

@@ -0,0 +1,85 @@
+package wacc
+
+import org.scalatest.flatspec.AnyFlatSpec
+
+class LabelGeneratorSpec extends AnyFlatSpec {
+  import microWacc._
+  import assemblyIR.{LabelDef, LabelArg, Directive}
+  import types.?
+
+  "getLabel" should "return unique labels" in {
+    val labelGenerator = new LabelGenerator
+    val labels = (1 to 10).map(_ => labelGenerator.getLabel())
+    assert(labels.distinct.length == labels.length)
+  }
+
+  "getLabelDef" should "return unique labels" in {
+    assert(
+      LabelDef("test") == LabelDef("test") &&
+        LabelDef("test").hashCode == LabelDef("test").hashCode,
+      "Sanity check: LabelDef should be case-classes"
+    )
+
+    val labelGenerator = new LabelGenerator
+    val labels = (List(
+      Builtin.Exit,
+      Builtin.Printf,
+      Ident("exit", 0)(?),
+      Ident("test", 0)(?)
+    ) ++ RuntimeError.all.toList).map(labelGenerator.getLabelDef(_))
+    assert(labels.distinct.length == labels.length)
+  }
+
+  "getLabelArg" should "return unique labels" in {
+    assert(
+      LabelArg("test") == LabelArg("test") &&
+        LabelArg("test").hashCode == LabelArg("test").hashCode,
+      "Sanity check: LabelArg should be case-classes"
+    )
+
+    val labelGenerator = new LabelGenerator
+    val labels = (List(
+      Builtin.Exit,
+      Builtin.Printf,
+      Ident("exit", 0)(?),
+      Ident("test", 0)(?),
+      "test",
+      "test",
+      "test3"
+    ) ++ RuntimeError.all.toList).map {
+      case s: String                      => labelGenerator.getLabelArg(s)
+      case t: (CallTarget | RuntimeError) => labelGenerator.getLabelArg(t)
+    }
+    assert(labels.distinct.length == labels.distinct.length)
+  }
+
+  it should "return consistent labels to getLabelDef" in {
+    val labelGenerator = new LabelGenerator
+    val targets = (List(
+      Builtin.Exit,
+      Builtin.Printf,
+      Ident("exit", 0)(?),
+      Ident("test", 0)(?)
+    ) ++ RuntimeError.all.toList)
+    val labelDefs = targets.map(labelGenerator.getLabelDef(_).toString.dropRight(1)).toSet
+    val labelArgs = targets.map(labelGenerator.getLabelArg(_).toString).toSet
+    assert(labelDefs == labelArgs)
+  }
+
+  "generateConstants" should "generate de-duplicated labels for strings" in {
+    val labelGenerator = new LabelGenerator
+    val strings = List("hello", "world", "hello\u0000world", "hello", "Hello")
+    val distincts = strings.distinct.length
+    val labels = strings.map(labelGenerator.getLabelArg(_).toString).toSet
+    val asmLines = labelGenerator.generateConstants
+    assert(
+      asmLines.collect { case LabelDef(name) =>
+        name
+      }.length == distincts
+    )
+    assert(
+      asmLines.collect { case Directive.Asciz(str) => str }.length == distincts
+    )
+    assert(asmLines.collect { case LabelDef(name) => name }.toList.toSet == labels)
+  }
+}

src/test/wacc/backend/stackSpec.scala

@@ -0,0 +1,140 @@
+package wacc
+
+import org.scalatest.flatspec.AnyFlatSpec
+import cats.data.Chain
+
+class StackSpec extends AnyFlatSpec {
+  import microWacc._
+  import assemblyIR._
+  import assemblyIR.Size._
+  import assemblyIR.commonRegisters._
+  import types.{KnownType, ?}
+  import sizeExtensions.size
+
+  private val RSP = Register(Q64, RegName.SP)
+
+  "size" should "be 0 initially" in {
+    val stack = new Stack
+    assert(stack.size == 0)
+  }
+
+  "push" should "add an expression to the stack" in {
+    val stack = new Stack
+    val expr = Ident("x", 0)(?)
+    val result = stack.push(expr, RAX)
+    assert(stack.size == 1)
+    assert(result == Push(RAX))
+  }
+
+  it should "add 2 expressions to the stack" in {
+    val stack = new Stack
+    val expr1 = Ident("x", 0)(?)
+    val expr2 = Ident("x", 1)(?)
+    val result1 = stack.push(expr1, RAX)
+    val result2 = stack.push(expr2, RCX)
+    assert(stack.size == 2)
+    assert(result1 == Push(RAX))
+    assert(result2 == Push(RCX))
+  }
+
+  it should "add a value to the stack" in {
+    val stack = new Stack
+    val result = stack.push(D32, RAX)
+    assert(stack.size == 1)
+    assert(result == Push(RAX))
+  }
+
+  "reserve" should "reserve space for an identifier" in {
+    val stack = new Stack
+    val ident = Ident("x", 0)(KnownType.Int)
+    val result = stack.reserve(ident)
+    assert(stack.size == 1)
+    assert(result == Subtract(RSP, ImmediateVal(Q64.toInt)))
+  }
+
+  it should "reserve space for a register" in {
+    val stack = new Stack
+    val result = stack.reserve(RAX)
+    assert(stack.size == 1)
+    assert(result == Subtract(RSP, ImmediateVal(Q64.toInt)))
+  }
+
+  it should "reserve space for multiple values" in {
+    val stack = new Stack
+    val result = stack.reserve(D32, Q64, B8)
+    assert(stack.size == 3)
+    assert(result == Subtract(RSP, ImmediateVal(Q64.toInt * 3)))
+  }
+
+  "pop" should "remove the last value from the stack" in {
+    val stack = new Stack
+    stack.push(D32, RAX)
+    val result = stack.pop(RAX)
+    assert(stack.size == 0)
+    assert(result == Pop(RAX))
+  }
+
+  "drop" should "remove the last 2 value from the stack" in {
+    val stack = new Stack
+    stack.push(D32, RAX)
+    stack.push(Q64, RAX)
+    stack.push(B8, RAX)
+    val result = stack.drop(2)
+    assert(stack.size == 1)
+    assert(result == Add(RSP, ImmediateVal(Q64.toInt * 2)))
+  }
+
+  "withScope" should "reset stack after block" in {
+    val stack = new Stack
+    stack.push(D32, RAX)
+    stack.push(Q64, RCX)
+    stack.push(B8, RDX)
+    val result = stack.withScope(() =>
+      Chain(
+        stack.push(Q64, RSI),
+        stack.push(B8, RDI),
+        stack.push(B8, RBP)
+      )
+    )
+    assert(stack.size == 3)
+    assert(
+      result == Chain(
+        Push(RSI),
+        Push(RDI),
+        Push(RBP),
+        Add(RSP, ImmediateVal(Q64.toInt * 3))
+      )
+    )
+  }
+
+  "accessVar" should "return the correctly-sized memory location for the identifier" in {
+    val stack = new Stack
+    val id = Ident("x", 0)(KnownType.Int)
+    stack.push(Q64, RAX)
+    stack.push(id, RCX)
+    stack.push(B8, RDX)
+    stack.push(D32, RSI)
+    val result = stack.accessVar(Ident("x", 0)(KnownType.Int))
+    assert(result == MemLocation(RSP, Q64.toInt * 2, opSize = Some(KnownType.Int.size)))
+  }
+
+  "contains" should "return true if the stack contains the identifier" in {
+    val stack = new Stack
+    val id = Ident("x", 0)(KnownType.Int)
+    stack.push(D32, RAX)
+    stack.push(id, RCX)
+    stack.push(B8, RDX)
+    assert(stack.contains(id))
+    assert(!stack.contains(Ident("x", 1)(KnownType.Int)))
+  }
+
+  "head" should "return the correct memory location for the last element" in {
+    val stack = new Stack
+    val id = Ident("x", 0)(KnownType.Int)
+    stack.push(D32, RAX)
+    stack.push(id, RCX)
+    stack.push(B8, RDX)
+    val result = stack.head
+    assert(result == MemLocation(RSP, opSize = Some(B8)))
+  }
+}

src/test/wacc/examples.scala

@@ -1,10 +1,19 @@
 package wacc
 
-import org.scalatest.{ParallelTestExecution, BeforeAndAfterAll}
-import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.BeforeAndAfterAll
 import org.scalatest.Inspectors.forEvery
+import org.scalatest.matchers.should.Matchers._
+import org.scalatest.freespec.AsyncFreeSpec
+import cats.effect.testing.scalatest.AsyncIOSpec
+import java.io.File
+import java.nio.file.Path
+import sys.process._
+import scala.io.Source
+import cats.effect.IO
+import wacc.{compile as compileWacc}
+
+class ParallelExamplesSpec extends AsyncFreeSpec with AsyncIOSpec with BeforeAndAfterAll {
 
-class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll with ParallelTestExecution {
   val files =
     allWaccFiles("wacc-examples/valid").map { p =>
       (p.toString, List(0))
@@ -17,73 +26,119 @@ class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll with Paral
       } ++
       allWaccFiles("wacc-examples/invalid/whack").map { p =>
         (p.toString, List(100, 200))
+      } ++
+      allWaccFiles("extension/examples/valid").map { p =>
+        (p.toString, List(0))
+      } ++
+      allWaccFiles("extension/examples/invalid/syntax").map { p =>
+        (p.toString, List(100))
+      } ++
+      allWaccFiles("extension/examples/invalid/semantics").map { p =>
+        (p.toString, List(200))
       }
 
-  // tests go here
-  forEvery(files.filter { (filename, _) =>
-    !fileIsDissallowed(filename)
-  }) { (filename, expectedResult) =>
-    s"$filename" should "be parsed with correct result" in {
-      val contents = os.read(os.Path(filename))
-      assert(expectedResult.contains(compile(contents)))
+  forEvery(files) { (filename, expectedResult) =>
+    val baseFilename = filename.stripSuffix(".wacc")
+
+    s"$filename" - {
+      "should be compiled with correct result" in {
+        if (fileIsPendingFrontend(filename))
+          IO.pure(pending)
+        else
+          compileWacc(Path.of(filename), outputDir = None, log = false).map { result =>
+            expectedResult should contain(result)
+          }
+      }
+
+      if (expectedResult == List(0)) {
+        "should run with correct result" in {
+          if (fileIsDisallowedBackend(filename))
+            IO.pure(succeed)
+          else if (fileIsPendingBackend(filename))
+            IO.pure(pending)
+          else
+            for {
+              contents <- IO(Source.fromFile(File(filename)).getLines.toList)
+              inputLine = extractInput(contents)
+              expectedOutput = extractOutput(contents)
+              expectedExit = extractExit(contents)
+
+              asmFilename = baseFilename + ".s"
+              execFilename = baseFilename
+              gccResult <- IO(s"gcc -o $execFilename -z noexecstack $asmFilename".!)
+
+              _ = assert(gccResult == 0)
+
+              stdout <- IO.pure(new StringBuilder)
+              process <- IO {
+                s"timeout 5s $execFilename" run ProcessIO(
+                  in = w => {
+                    w.write(inputLine.getBytes)
+                    w.close()
+                  },
+                  out = Source.fromInputStream(_).addString(stdout),
+                  err = _ => ()
+                )
+              }
+
+              exitCode <- IO.pure(process.exitValue)
+
+            } yield {
+              exitCode shouldBe expectedExit
+              normalizeOutput(stdout.toString) shouldBe expectedOutput
+            }
+        }
+      }
     }
   }
 
   def allWaccFiles(dir: String): IndexedSeq[os.Path] =
     val d = java.io.File(dir)
-    os.walk(os.Path(d.getAbsolutePath)).filter { _.ext == "wacc" }
+    os.walk(os.Path(d.getAbsolutePath)).filter(_.ext == "wacc")
 
-  def fileIsDissallowed(filename: String): Boolean =
-    Seq(
-      // format: off
-      // disable formatting to avoid binPack
-      // "wacc-examples/valid/advanced",
-      // "wacc-examples/valid/array",
-      // "wacc-examples/valid/basic/exit",
-      // "wacc-examples/valid/basic/skip",
-      // "wacc-examples/valid/expressions",
-      // "wacc-examples/valid/function/nested_functions",
-      // "wacc-examples/valid/function/simple_functions",
-      // "wacc-examples/valid/if",
-      // "wacc-examples/valid/IO/print",
-      // "wacc-examples/valid/IO/read",
-      // "wacc-examples/valid/IO/IOLoop.wacc",
-      // "wacc-examples/valid/IO/IOSequence.wacc",
-      // "wacc-examples/valid/pairs",
-      // "wacc-examples/valid/runtimeErr",
-      // "wacc-examples/valid/scope",
-      // "wacc-examples/valid/sequence",
-      // "wacc-examples/valid/variables",
-      // "wacc-examples/valid/while",
-      // invalid (syntax)
-      // "wacc-examples/invalid/syntaxErr/array",
-      // "wacc-examples/invalid/syntaxErr/basic",
-      // "wacc-examples/invalid/syntaxErr/expressions",
-      // "wacc-examples/invalid/syntaxErr/function",
-      // "wacc-examples/invalid/syntaxErr/if",
-      // "wacc-examples/invalid/syntaxErr/literals",
-      // "wacc-examples/invalid/syntaxErr/pairs",
-      // "wacc-examples/invalid/syntaxErr/print",
-      // "wacc-examples/invalid/syntaxErr/sequence",
-      // "wacc-examples/invalid/syntaxErr/variables",
-      // "wacc-examples/invalid/syntaxErr/while",
-      // invalid (semantic)
-      // "wacc-examples/invalid/semanticErr/array",
-      // "wacc-examples/invalid/semanticErr/exit",
-      // "wacc-examples/invalid/semanticErr/expressions",
-      // "wacc-examples/invalid/semanticErr/function",
-      // "wacc-examples/invalid/semanticErr/if",
-      // "wacc-examples/invalid/semanticErr/IO",
-      // "wacc-examples/invalid/semanticErr/multiple",
-      // "wacc-examples/invalid/semanticErr/pairs",
-      // "wacc-examples/invalid/semanticErr/print",
-      // "wacc-examples/invalid/semanticErr/read",
-      // "wacc-examples/invalid/semanticErr/scope",
-      // "wacc-examples/invalid/semanticErr/variables",
-      // "wacc-examples/invalid/semanticErr/while",
-      // invalid (whack)
-      // "wacc-examples/invalid/whack"
-      // format: on
-      // format: on
-    ).find(filename.contains).isDefined
+  private def fileIsDisallowedBackend(filename: String): Boolean =
+    filename.matches("^.*wacc-examples/valid/advanced.*$")
+
+  private def fileIsPendingFrontend(filename: String): Boolean =
+    List(
+      // "^.*extension/examples/invalid/syntax/imports/importBadSyntax.*$",
+      // "^.*extension/examples/invalid/semantics/imports.*$",
+      // "^.*extension/examples/valid/imports.*$"
+    ).exists(filename.matches)
+
+  private def fileIsPendingBackend(filename: String): Boolean =
+    List(
+      // "^.*extension/examples/invalid/syntax/imports.*$",
+      // "^.*extension/examples/invalid/semantics/imports.*$",
+      // "^.*extension/examples/valid/imports.*$"
+    ).exists(filename.matches)
+
+  private def extractInput(contents: List[String]): String =
+    contents
+      .find(_.matches("^# ?[Ii]nput:.*$"))
+      .map(_.split(":").last.strip + "\n")
+      .getOrElse("")
+
+  private def extractOutput(contents: List[String]): String = {
+    val outputLineIdx = contents.indexWhere(_.matches("^# ?[Oo]utput:.*$"))
+    if (outputLineIdx == -1) ""
+    else
+      contents
+        .drop(outputLineIdx + 1)
+        .takeWhile(_.startsWith("#"))
+        .map(_.stripPrefix("#").stripLeading)
+        .mkString("\n")
+  }
+
+  private def extractExit(contents: List[String]): Int = {
+    val exitLineIdx = contents.indexWhere(_.matches("^# ?[Ee]xit:.*$"))
+    if (exitLineIdx == -1) 0
+    else contents(exitLineIdx + 1).stripPrefix("#").strip.toInt
+  }
+
+  private def normalizeOutput(output: String): String =
+    output
+      .replaceAll("0x[0-9a-f]+", "#addrs#")
+      .replaceAll("fatal error:.*", "#runtime_error#\u0000")
+      .takeWhile(_ != '\u0000')
 }

wacc-syntax/.vscodeignore

@@ -0,0 +1,4 @@
+.vscode/**
+.vscode-test/**
+.gitignore
+vsc-extension-quickstart.md

wacc-syntax/CHANGELOG.md

@@ -0,0 +1,9 @@
+# Change Log
+
+All notable changes to the "wacc-syntax" extension will be documented in this file.
+
+Check [Keep a Changelog](http://keepachangelog.com/) for recommendations on how to structure this file.
+
+## [Unreleased]
+
+- Initial release

wacc-syntax/README.md

@@ -0,0 +1,7 @@
+### INTELLIWACC
+
+This is the IntelliWACC extension for WACC code development; featuring syntax highlighting, error messages/highlighting and imports.
+
+This extension was developed as a part of the "WACC Extensions" milestone 2025.
+
+Authored by Alex L, Gleb K, Guy C and Jonny T

wacc-syntax/extension.js

@@ -0,0 +1,71 @@
+// Developed using the VSC language extension tutorial
+// https://code.visualstudio.com/api/language-extensions/overview
+
+const vscode = require('vscode');
+const { execSync } = require('child_process');
+const { parse } = require('path');
+
+function activate(context) {
+    console.log('IntelliWACC is now active!');
+
+    let diagnosticCollection = vscode.languages.createDiagnosticCollection('wacc');
+    context.subscriptions.push(diagnosticCollection);
+
+    vscode.workspace.onDidSaveTextDocument((document) => {
+        if (document.languageId !== 'wacc') return;
+
+        let diagnostics = [];
+        let errors = generateErrors(document.getText(), document.fileName);
+        errors.forEach(error => {
+            console.log(error);
+            let range = new vscode.Range(error.line - 1 , error.column - 1, error.line - 1, error.column + error.size);
+            let diagnostic = new vscode.Diagnostic(range, error.errorMessage, vscode.DiagnosticSeverity.Error);
+            diagnostics.push(diagnostic);
+        });
+
+        diagnosticCollection.set(document.uri, diagnostics);
+    });
+}
+
+function deactivate() {
+    console.log('IntelliWACC is deactivating...');
+}
+
+function generateErrors(code, filePath) {
+    try {
+        console.log("generating errors")
+        const fs = require('fs');
+        const tmpFilePath = parse(filePath).dir + '/.temp_wacc_file.wacc';
+        fs.writeFileSync(tmpFilePath, code);
+
+        let output;
+        try {
+            const waccExePath = `${__dirname}/wacc-compiler`;
+            output = execSync(`${waccExePath} ${tmpFilePath}`, { encoding: 'utf8', shell: true, stdio: 'pipe'});
+        } catch (err) {
+            console.log("Error running compiler");
+            output = err.stdout;
+            console.log(output);
+        } 
+        let errors = [];
+        errorRegex = /\(line ([\d]+), column ([\d]+)\):\n([^>]+)([^\^]+)([\^]+)\n([^\n]+)([^\(]*)/g
+        while((match = errorRegex.exec(output)) !== null) {
+            console.log(match[5]);
+            errors.push({
+                line: parseInt(match[1], 10),
+                column: parseInt(match[2], 10),
+                errorMessage: match[3].trim(),
+                size: match[5].length - 1
+            });
+        }
+        return errors;
+    } catch (err) {
+        console.error('Error running compiler:', err);
+        return [];
+    }
+}
+
+module.exports = {
+    activate,
+    deactivate
+};

wacc-syntax/language-configuration.json

@@ -0,0 +1,28 @@
+{
+    "comments": {
+        // symbol used for single line comment. Remove this entry if your language does not support line comments
+        "lineComment": "#",
+    },
+    // symbols used as brackets
+    "brackets": [
+        ["{", "}"],
+        ["[", "]"],
+        ["(", ")"]
+    ],
+    // symbols that are auto closed when typing
+    "autoClosingPairs": [
+        ["{", "}"],
+        ["[", "]"],
+        ["(", ")"],
+        ["\"", "\""],
+        ["'", "'"]
+    ],
+    // symbols that can be used to surround a selection
+    "surroundingPairs": [
+        ["{", "}"],
+        ["[", "]"],
+        ["(", ")"],
+        ["\"", "\""],
+        ["'", "'"]
+    ]
+}

wacc-syntax/package-lock.json

@@ -0,0 +1,15 @@
+{
+  "name": "wacc-syntax",
+  "version": "0.0.1",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "wacc-syntax",
+      "version": "0.0.1",
+      "engines": {
+        "vscode": "^1.97.0"
+      }
+    }
+  }
+}

wacc-syntax/package.json

@@ -0,0 +1,40 @@
+{
+  "name": "wacc-syntax",
+  "displayName": "intelliWACC",
+  "description": "WACC language support features",
+  "version": "0.0.1",
+  "publisher": "WACC-37-2025",
+  "icon": "icon.png",
+  "engines": {
+    "vscode": "^1.97.0"
+  },
+  "categories": [
+    "Programming Languages"
+  ],
+  "contributes": {
+    "languages": [{
+      "id": "wacc",
+      "aliases": ["WACC", "wacc"],
+      "extensions": [".wacc"],
+      "configuration": "./language-configuration.json"
+    }],
+    "grammars": [{
+      "language": "wacc",
+      "scopeName": "source.wacc",
+      "path": "./syntaxes/wacc.tmLanguage.json"
+    }],
+    "properties": {
+      "files.exclude": {
+        "type": "object",
+        "default": {
+          "**/.temp_wacc_file.*": true
+        },
+        "description": "Configure patterns for excluding files and folders."
+      }
+    }
+  },
+  "scripts": {
+    "build": "vsce package"
+  },
+  "main": "./extension.js"
+}

wacc-syntax/syntaxes/wacc.tmLanguage.json

@@ -0,0 +1,56 @@
+{
+	"$schema": "https://raw.githubusercontent.com/martinring/tmlanguage/master/tmlanguage.json",
+	"name": "WACC",
+	"scopeName": "source.wacc",
+	"fileTypes": [
+		"wacc"
+	],
+	"patterns": [
+		{
+			"match": "\\b(true|false)\\b",
+			"name": "keyword.constant.wacc"
+		},
+		{
+			"match": "\\b(int|bool|char|string|pair|null)\\b",
+			"name": "storage.type.wacc"
+		},
+		{
+			"match": "\".*?\"",
+      "name": "string.quoted.double.mylang"
+		},
+		{
+			"match": "\\b(begin|end)\\b",
+			"name": "keyword.other.unit"
+		},
+		{
+			"match": "\\b(if|then|else|fi|while|do|done|skip|is)\\b",
+			"name": "keyword.control.wacc"
+		},
+		{
+			"match": "\\b(read|free|print|println|newpair|call|fst|snd|ord|chr|len)\\b",
+			"name": "keyword.operator.function.wacc"
+		},
+		{
+			"match": "\\b(return|exit)\\b",
+			"name": "keyword.operator.wacc"
+		},
+		{
+			"match": "'[^']{1}'",
+			"name": "constant.character.wacc"
+		},
+		{
+      "match": "\\b([a-zA-Z_][a-zA-Z0-9_]*)\\s*(?=\\()",
+      "name": "variable.function.wacc"
+    },
+		{
+      "match": "\\b([a-zA-Z_][a-zA-Z0-9_]*)\\b",
+      "name": "variable.other.wacc"
+    },
+		{
+      "match": "#.*$",
+      "name": "comment.line"
+    }
+	
+	]
+
+}

wacc-syntax/vsc-extension-quickstart.md

@@ -0,0 +1,29 @@
+# Welcome to your VS Code Extension
+
+## What's in the folder
+
+* This folder contains all of the files necessary for your extension.
+* `package.json` - this is the manifest file in which you declare your language support and define the location of the grammar file that has been copied into your extension.
+* `syntaxes/wacc.tmLanguage.json` - this is the Text mate grammar file that is used for tokenization.
+* `language-configuration.json` - this is the language configuration, defining the tokens that are used for comments and brackets.
+
+## Get up and running straight away
+
+* Make sure the language configuration settings in `language-configuration.json` are accurate.
+* Press `F5` to open a new window with your extension loaded.
+* Create a new file with a file name suffix matching your language.
+* Verify that syntax highlighting works and that the language configuration settings are working.
+
+## Make changes
+
+* You can relaunch the extension from the debug toolbar after making changes to the files listed above.
+* You can also reload (`Ctrl+R` or `Cmd+R` on Mac) the VS Code window with your extension to load your changes.
+
+## Add more language features
+
+* To add features such as IntelliSense, hovers and validators check out the VS Code extenders documentation at https://code.visualstudio.com/docs
+
+## Install your extension
+
+* To start using your extension with Visual Studio Code copy it into the `<user home>/.vscode/extensions` folder and restart Code.
+* To share your extension with the world, read on https://code.visualstudio.com/docs about publishing an extension.

wacc.target

@@ -0,0 +1 @@
+x86-64