diff --git a/.commitlintrc.js b/.commitlintrc.js
new file mode 100644
index 0000000..a295b1d
--- /dev/null
+++ b/.commitlintrc.js
@@ -0,0 +1,4 @@
+export default {
+  extends: ['@commitlint/config-conventional'],
+  ignores: [commit => commit.startsWith("Local Mutable Chains\n")]
+}
diff --git a/.commitlintrc.yml b/.commitlintrc.yml
deleted file mode 100644
index 175ef04..0000000
--- a/.commitlintrc.yml
+++ /dev/null
@@ -1 +0,0 @@
-extends: "@commitlint/config-conventional"
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 98a6044..e61541c 100644
--- a/.gitlab-ci.yml
+++ b/.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
@@ -48,10 +49,10 @@ 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:
diff --git a/src/main/wacc/Main.scala b/src/main/wacc/Main.scala
index e8e7b7b..020cbcd 100644
--- a/src/main/wacc/Main.scala
+++ b/src/main/wacc/Main.scala
@@ -1,13 +1,13 @@
 package wacc
 
 import scala.collection.mutable
+import cats.data.Chain
 import parsley.{Failure, Success}
 import scopt.OParser
 import java.io.File
 import java.io.PrintStream
 
 import assemblyIR as asm
-import wacc.microWacc.IntLiter
 
 case class CliConfig(
     file: File = new File(".")
@@ -64,157 +64,8 @@ def frontend(
 }
 
 val s = "enter an integer to echo"
-def backend(typedProg: microWacc.Program): List[asm.AsmLine] | String =
-  typedProg match {
-    case microWacc.Program(
-          Nil,
-          microWacc.Call(microWacc.Builtin.Exit, microWacc.IntLiter(v) :: Nil) :: Nil
-        ) =>
-      s""".intel_syntax noprefix
-.globl main
-main:
-	mov edi, ${v}
-	call exit@plt
-"""
-    case microWacc.Program(
-          Nil,
-          microWacc.Assign(microWacc.Ident("x", _), microWacc.IntLiter(1)) ::
-          microWacc.Call(microWacc.Builtin.Println, _) ::
-          microWacc.Assign(
-            microWacc.Ident("x", _),
-            microWacc.Call(microWacc.Builtin.ReadInt, Nil)
-          ) ::
-          microWacc.Call(microWacc.Builtin.Println, microWacc.Ident("x", _) :: Nil) :: Nil
-        ) =>
-      """.intel_syntax noprefix
-.globl main
-.section .rodata
-# length of .L.str0
-	.int 24
-.L.str0:
-	.asciz "enter an integer to echo"
-.text
-main:
-	push rbp
-	# push {rbx, r12}
-	sub rsp, 16
-	mov qword ptr [rsp], rbx
-	mov qword ptr [rsp + 8], r12
-	mov rbp, rsp
-	mov r12d, 1
-	lea rdi, [rip + .L.str0]
-	# statement primitives do not return results (but will clobber r0/rax)
-	call _prints
-	call _println
-	# load the current value in the destination of the read so it supports defaults
-	mov edi, r12d
-	call _readi
-	mov r12d, eax
-	mov edi, eax
-	# statement primitives do not return results (but will clobber r0/rax)
-	call _printi
-	call _println
-	mov rax, 0
-	# pop/peek {rbx, r12}
-	mov rbx, qword ptr [rsp]
-	mov r12, qword ptr [rsp + 8]
-	add rsp, 16
-	pop rbp
-	ret
-
-.section .rodata
-# length of .L._printi_str0
-	.int 2
-.L._printi_str0:
-	.asciz "%d"
-.text
-_printi:
-	push rbp
-	mov rbp, rsp
-	# external calls must be stack-aligned to 16 bytes, accomplished by masking with fffffffffffffff0
-	and rsp, -16
-	mov esi, edi
-	lea rdi, [rip + .L._printi_str0]
-	# on x86, al represents the number of SIMD registers used as variadic arguments
-	mov al, 0
-	call printf@plt
-	mov rdi, 0
-	call fflush@plt
-	mov rsp, rbp
-	pop rbp
-	ret
-
-.section .rodata
-# length of .L._prints_str0
-	.int 4
-.L._prints_str0:
-	.asciz "%.*s"
-.text
-_prints:
-	push rbp
-	mov rbp, rsp
-	# external calls must be stack-aligned to 16 bytes, accomplished by masking with fffffffffffffff0
-	and rsp, -16
-	mov rdx, rdi
-	mov esi, dword ptr [rdi - 4]
-	lea rdi, [rip + .L._prints_str0]
-	# on x86, al represents the number of SIMD registers used as variadic arguments
-	mov al, 0
-	call printf@plt
-	mov rdi, 0
-	call fflush@plt
-	mov rsp, rbp
-	pop rbp
-	ret
-
-.section .rodata
-# length of .L._println_str0
-	.int 0
-.L._println_str0:
-	.asciz ""
-.text
-_println:
-	push rbp
-	mov rbp, rsp
-	# external calls must be stack-aligned to 16 bytes, accomplished by masking with fffffffffffffff0
-	and rsp, -16
-	lea rdi, [rip + .L._println_str0]
-	call puts@plt
-	mov rdi, 0
-	call fflush@plt
-	mov rsp, rbp
-	pop rbp
-	ret
-
-.section .rodata
-# length of .L._readi_str0
-	.int 2
-.L._readi_str0:
-	.asciz "%d"
-.text
-_readi:
-	push rbp
-	mov rbp, rsp
-	# external calls must be stack-aligned to 16 bytes, accomplished by masking with fffffffffffffff0
-	and rsp, -16
-	# RDI contains the "original" value of the destination of the read
-	# allocate space on the stack to store the read: preserve alignment!
-	# the passed default argument should be stored in case of EOF
-	sub rsp, 16
-	mov dword ptr [rsp], edi
-	lea rsi, qword ptr [rsp]
-	lea rdi, [rip + .L._readi_str0]
-	# on x86, al represents the number of SIMD registers used as variadic arguments
-	mov al, 0
-	call scanf@plt
-	mov eax, dword ptr [rsp]
-	add rsp, 16
-	mov rsp, rbp
-	pop rbp
-	ret
-    """
-    case _ => List()
-  }
+def backend(typedProg: microWacc.Program): Chain[asm.AsmLine] =
+  asmGenerator.generateAsm(typedProg)
 
 def compile(filename: String, outFile: Option[File] = None)(using
     stdout: PrintStream = Console.out
@@ -222,13 +73,8 @@ def compile(filename: String, outFile: Option[File] = None)(using
   frontend(os.read(os.Path(filename))) match {
     case Left(typedProg) =>
       val asmFile = outFile.getOrElse(File(filename.stripSuffix(".wacc") + ".s"))
-      backend(typedProg) match {
-        case s: String =>
-          os.write.over(os.Path(asmFile.getAbsolutePath), s)
-        case ops: List[asm.AsmLine] => {
-          writer.writeTo(ops, PrintStream(asmFile))
-        }
-      }
+      val asm = backend(typedProg)
+      writer.writeTo(asm, PrintStream(asmFile))
       0
     case Right(exitCode) => exitCode
   }
diff --git a/src/main/wacc/backend/Stack.scala b/src/main/wacc/backend/Stack.scala
new file mode 100644
index 0000000..94b329a
--- /dev/null
+++ b/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(src.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 IndexAddress for a variable in the stack. */
+  def accessVar(ident: mw.Ident): IndexAddress =
+    IndexAddress(RSP, sizeBytes - stack(ident).bottom)
+
+  def contains(ident: mw.Ident): Boolean = stack.contains(ident)
+  def head: MemLocation = MemLocation(RSP, stack.last._2.size)
+
+  override def toString(): String = stack.toString
+}
diff --git a/src/main/wacc/backend/asmGenerator.scala b/src/main/wacc/backend/asmGenerator.scala
new file mode 100644
index 0000000..60e0b47
--- /dev/null
+++ b/src/main/wacc/backend/asmGenerator.scala
@@ -0,0 +1,458 @@
+package wacc
+
+import scala.collection.mutable.ListBuffer
+import cats.data.Chain
+import cats.syntax.foldable._
+
+object asmGenerator {
+  import microWacc._
+  import assemblyIR._
+  import assemblyIR.Size._
+  import assemblyIR.RegName._
+  import types._
+  import sizeExtensions._
+  import lexer.escapedChars
+
+  abstract case class Error() {
+    def strLabel: String
+    def errStr: String
+    def errLabel: String
+
+    def stringDef: Chain[AsmLine] = Chain(
+      Directive.Int(errStr.size),
+      LabelDef(strLabel),
+      Directive.Asciz(errStr)
+    )
+  }
+  object zeroDivError extends Error {
+    // TODO: is this bad? Can we make an error case class/some other structure?
+    def strLabel = ".L._errDivZero_str0"
+    def errStr = "fatal error: division or modulo by zero"
+    def errLabel = ".L._errDivZero"
+  }
+
+  private val RAX = Register(Q64, AX)
+  private val EAX = Register(D32, AX)
+  private val RDI = Register(Q64, DI)
+  private val RIP = Register(Q64, IP)
+  private val RBP = Register(Q64, BP)
+  private val RSI = Register(Q64, SI)
+  private val RDX = Register(Q64, DX)
+  private val RCX = Register(Q64, CX)
+  private val argRegs = List(DI, SI, DX, CX, R8, R9)
+
+  extension [T](chain: Chain[T])
+    def +(item: T): Chain[T] = chain.append(item)
+
+    def concatAll(chains: Chain[T]*): Chain[T] =
+      chains.foldLeft(chain)(_ ++ _)
+
+  class LabelGenerator {
+    var labelVal = -1
+    def getLabel(): String = {
+      labelVal += 1
+      s".L$labelVal"
+    }
+    def getLabel(target: CallTarget): String = target match {
+      case Ident(v, _)   => s"wacc_$v"
+      case Builtin(name) => s"_$name"
+    }
+  }
+
+  def generateAsm(microProg: Program): Chain[AsmLine] = {
+    given stack: Stack = Stack()
+    given strings: ListBuffer[String] = ListBuffer[String]()
+    given labelGenerator: LabelGenerator = LabelGenerator()
+    val Program(funcs, main) = microProg
+
+    val progAsm = Chain(LabelDef("main")).concatAll(
+      funcPrologue(),
+      main.foldMap(generateStmt(_)),
+      Chain.one(Xor(RAX, RAX)),
+      funcEpilogue(),
+      generateBuiltInFuncs(),
+      funcs.foldMap(generateUserFunc(_))
+    )
+
+    val strDirs = strings.toList.zipWithIndex.foldMap { case (str, i) =>
+      Chain(
+        Directive.Int(str.size),
+        LabelDef(s".L.str$i"),
+        Directive.Asciz(str.escaped)
+      )
+    } ++ zeroDivError.stringDef
+
+    Chain(
+      Directive.IntelSyntax,
+      Directive.Global("main"),
+      Directive.RoData
+    ).concatAll(
+      strDirs,
+      Chain.one(Directive.Text),
+      progAsm
+    )
+  }
+
+  private def wrapBuiltinFunc(labelName: String, funcBody: Chain[AsmLine])(using
+      stack: Stack
+  ): Chain[AsmLine] = {
+    var chain = Chain.one[AsmLine](LabelDef(labelName))
+    chain ++= funcPrologue()
+    chain ++= funcBody
+    chain ++= funcEpilogue()
+    chain
+  }
+
+  private def generateUserFunc(func: FuncDecl)(using
+      strings: ListBuffer[String],
+      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(Q64) // Reserve return pointer slot
+    var chain = Chain.one[AsmLine](LabelDef(labelGenerator.getLabel(func.name)))
+    chain ++= funcPrologue()
+    // Push the rest of params onto the stack for simplicity
+    argRegs.zip(func.params).foreach { (reg, param) =>
+      chain += stack.push(param, Register(Q64, reg))
+    }
+    chain ++= func.body.foldMap(generateStmt(_))
+    // No need for epilogue here since all user functions must return explicitly
+    chain
+  }
+
+  private def generateBuiltInFuncs()(using
+      stack: Stack,
+      labelGenerator: LabelGenerator
+  ): Chain[AsmLine] = {
+    var chain = Chain.empty[AsmLine]
+
+    chain ++= wrapBuiltinFunc(
+      labelGenerator.getLabel(Builtin.Exit),
+      Chain(stackAlign, assemblyIR.Call(CLibFunc.Exit))
+    )
+
+    chain ++= wrapBuiltinFunc(
+      labelGenerator.getLabel(Builtin.Printf),
+      Chain(
+        stackAlign,
+        assemblyIR.Call(CLibFunc.PrintF),
+        Xor(RDI, RDI),
+        assemblyIR.Call(CLibFunc.Fflush)
+      )
+    )
+
+    chain ++= wrapBuiltinFunc(
+      labelGenerator.getLabel(Builtin.PrintCharArray),
+      Chain(
+        stackAlign,
+        Load(RDX, IndexAddress(RSI, KnownType.Int.size.toInt)),
+        Move(Register(D32, SI), MemLocation(RSI, D32)),
+        assemblyIR.Call(CLibFunc.PrintF),
+        Xor(RDI, RDI),
+        assemblyIR.Call(CLibFunc.Fflush)
+      )
+    )
+
+    chain ++= wrapBuiltinFunc(
+      labelGenerator.getLabel(Builtin.Malloc),
+      Chain(stackAlign, assemblyIR.Call(CLibFunc.Malloc))
+      // Out of memory check is optional
+    )
+
+    chain ++= wrapBuiltinFunc(labelGenerator.getLabel(Builtin.Free), Chain.empty)
+
+    chain ++= wrapBuiltinFunc(
+      labelGenerator.getLabel(Builtin.Read),
+      Chain(
+        stackAlign,
+        Subtract(Register(Q64, SP), ImmediateVal(8)),
+        Push(RSI),
+        Load(RSI, MemLocation(Register(Q64, SP), Q64)),
+        assemblyIR.Call(CLibFunc.Scanf),
+        Pop(RAX)
+      )
+    )
+
+    chain ++= Chain(
+      // TODO can this be done with a call to generateStmt?
+      // Consider other error cases -> look to generalise
+      LabelDef(zeroDivError.errLabel),
+      stackAlign,
+      Load(RDI, IndexAddress(RIP, LabelArg(zeroDivError.strLabel))),
+      assemblyIR.Call(CLibFunc.PrintF),
+      Move(RDI, ImmediateVal(-1)),
+      assemblyIR.Call(CLibFunc.Exit)
+    )
+
+    chain
+  }
+
+  private def generateStmt(stmt: Stmt)(using
+      stack: Stack,
+      strings: ListBuffer[String],
+      labelGenerator: LabelGenerator
+  ): Chain[AsmLine] = {
+    var chain = Chain.empty[AsmLine]
+    chain += Comment(stmt.toString)
+    stmt match {
+      case Assign(lhs, rhs) =>
+        lhs match {
+          case ident: Ident =>
+            if (!stack.contains(ident)) chain += stack.reserve(ident)
+            chain ++= evalExprOntoStack(rhs)
+            chain += stack.pop(RAX)
+            chain += Move(stack.accessVar(ident), RAX)
+          case ArrayElem(x, i) =>
+            chain ++= evalExprOntoStack(rhs)
+            chain ++= evalExprOntoStack(i)
+            chain ++= evalExprOntoStack(x)
+            chain += stack.pop(RAX)
+            chain += stack.pop(RCX)
+            chain += stack.pop(RDX)
+
+            chain += Move(
+              IndexAddress(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()
+
+        chain ++= evalExprOntoStack(cond)
+        chain += stack.pop(RAX)
+        chain += Compare(RAX, ImmediateVal(0))
+        chain += Jump(LabelArg(elseLabel), Cond.Equal)
+
+        chain ++= stack.withScope(() => thenBranch.foldMap(generateStmt))
+        chain += Jump(LabelArg(endLabel))
+        chain += LabelDef(elseLabel)
+
+        chain ++= stack.withScope(() => elseBranch.foldMap(generateStmt))
+        chain += LabelDef(endLabel)
+
+      case While(cond, body) =>
+        val startLabel = labelGenerator.getLabel()
+        val endLabel = labelGenerator.getLabel()
+
+        chain += LabelDef(startLabel)
+        chain ++= evalExprOntoStack(cond)
+        chain += stack.pop(RAX)
+        chain += Compare(RAX, ImmediateVal(0))
+        chain += Jump(LabelArg(endLabel), Cond.Equal)
+
+        chain ++= stack.withScope(() => body.foldMap(generateStmt))
+        chain += Jump(LabelArg(startLabel))
+        chain += LabelDef(endLabel)
+
+      case call: microWacc.Call =>
+        chain ++= generateCall(call, isTail = false)
+
+      case microWacc.Return(expr) =>
+        expr match {
+          case call: microWacc.Call =>
+            chain ++= generateCall(call, isTail = true) // tco
+          case _ =>
+            chain ++= evalExprOntoStack(expr)
+            chain += stack.pop(RAX)
+            chain ++= funcEpilogue()
+        }
+    }
+
+    chain
+  }
+
+  private def evalExprOntoStack(expr: Expr)(using
+      stack: Stack,
+      strings: ListBuffer[String],
+      labelGenerator: LabelGenerator
+  ): Chain[AsmLine] = {
+    var chain = Chain.empty[AsmLine]
+    val stackSizeStart = stack.size
+    expr match {
+      case IntLiter(v)  => chain += stack.push(KnownType.Int.size, ImmediateVal(v))
+      case CharLiter(v) => chain += stack.push(KnownType.Char.size, ImmediateVal(v.toInt))
+      case ident: Ident => chain += stack.push(ident.ty.size, stack.accessVar(ident))
+
+      case array @ ArrayLiter(elems) =>
+        expr.ty match {
+          case KnownType.String =>
+            strings += elems.collect { case CharLiter(v) => v }.mkString
+            chain += Load(RAX, IndexAddress(RIP, LabelArg(s".L.str${strings.size - 1}")))
+            chain += stack.push(Q64, RAX)
+          case ty =>
+            chain ++= generateCall(
+              microWacc.Call(Builtin.Malloc, List(IntLiter(array.heapSize))),
+              isTail = false
+            )
+            chain += stack.push(Q64, RAX)
+            // Store the length of the array at the start
+            chain += Move(MemLocation(RAX, D32), ImmediateVal(elems.size))
+            elems.zipWithIndex.foldMap { (elem, i) =>
+              chain ++= evalExprOntoStack(elem)
+              chain += stack.pop(RCX)
+              chain += stack.pop(RAX)
+              chain += Move(IndexAddress(RAX, 4 + i * ty.elemSize.toInt), Register(ty.elemSize, CX))
+              chain += stack.push(Q64, RAX)
+            }
+        }
+
+      case BoolLiter(true) =>
+        chain += stack.push(KnownType.Bool.size, ImmediateVal(1))
+      case BoolLiter(false) =>
+        chain += Xor(RAX, RAX)
+        chain += stack.push(KnownType.Bool.size, RAX)
+      case NullLiter() =>
+        chain += stack.push(KnownType.Pair(?, ?).size, ImmediateVal(0))
+      case ArrayElem(x, i) =>
+        chain ++= evalExprOntoStack(x)
+        chain ++= evalExprOntoStack(i)
+        chain += stack.pop(RCX)
+        chain += stack.pop(RAX)
+        // + Int because we store the length of the array at the start
+        chain += Move(
+          Register(x.ty.elemSize, AX),
+          IndexAddress(RAX, KnownType.Int.size.toInt, RCX, x.ty.elemSize.toInt)
+        )
+        chain += stack.push(x.ty.elemSize, RAX)
+      case UnaryOp(x, op) =>
+        chain ++= evalExprOntoStack(x)
+        op match {
+          case UnaryOperator.Chr | UnaryOperator.Ord => // No op needed
+          case UnaryOperator.Len =>
+            chain += stack.pop(RAX)
+            chain += Move(EAX, MemLocation(RAX, D32))
+            chain += stack.push(D32, RAX)
+          case UnaryOperator.Negate =>
+            chain += Negate(stack.head)
+          case UnaryOperator.Not =>
+            chain += Xor(stack.head, ImmediateVal(1))
+        }
+
+      case BinaryOp(x, y, op) =>
+        val destX = Register(x.ty.size, AX)
+        chain ++= evalExprOntoStack(y)
+        chain ++= evalExprOntoStack(x)
+        chain += stack.pop(RAX)
+
+        op match {
+          case BinaryOperator.Add =>
+            chain += Add(stack.head, destX)
+          case BinaryOperator.Sub =>
+            chain += Subtract(destX, stack.head)
+            chain += stack.drop()
+            chain += stack.push(destX.size, RAX)
+          case BinaryOperator.Mul =>
+            chain += Multiply(destX, stack.head)
+            chain += stack.drop()
+            chain += stack.push(destX.size, RAX)
+
+          case BinaryOperator.Div =>
+            chain += Compare(stack.head, ImmediateVal(0))
+            chain += Jump(LabelArg(zeroDivError.errLabel), Cond.Equal)
+            chain += CDQ()
+            chain += Divide(stack.head)
+            chain += stack.drop()
+            chain += stack.push(destX.size, RAX)
+
+          case BinaryOperator.Mod =>
+            chain += CDQ()
+            chain += Divide(stack.head)
+            chain += stack.drop()
+            chain += stack.push(destX.size, RDX)
+
+          case BinaryOperator.Eq        => chain ++= generateComparison(destX, Cond.Equal)
+          case BinaryOperator.Neq       => chain ++= generateComparison(destX, Cond.NotEqual)
+          case BinaryOperator.Greater   => chain ++= generateComparison(destX, Cond.Greater)
+          case BinaryOperator.GreaterEq => chain ++= generateComparison(destX, Cond.GreaterEqual)
+          case BinaryOperator.Less      => chain ++= generateComparison(destX, Cond.Less)
+          case BinaryOperator.LessEq    => chain ++= generateComparison(destX, Cond.LessEqual)
+          case BinaryOperator.And       => chain += And(stack.head, destX)
+          case BinaryOperator.Or        => chain += Or(stack.head, destX)
+        }
+
+      case call: microWacc.Call =>
+        chain ++= generateCall(call, isTail = false)
+        chain += stack.push(call.ty.size, RAX)
+    }
+
+    assert(stack.size == stackSizeStart + 1)
+    chain ++= zeroRest(MemLocation(stack.head.pointer, Q64), expr.ty.size)
+    chain
+  }
+
+  private def generateCall(call: microWacc.Call, isTail: Boolean)(using
+      stack: Stack,
+      strings: ListBuffer[String],
+      labelGenerator: LabelGenerator
+  ): Chain[AsmLine] = {
+    var chain = Chain.empty[AsmLine]
+    val microWacc.Call(target, args) = call
+
+    argRegs.zip(args).foldMap { (reg, expr) =>
+      chain ++= evalExprOntoStack(expr)
+      chain += stack.pop(Register(Q64, reg))
+    }
+
+    args.drop(argRegs.size).foldMap {
+      chain ++= evalExprOntoStack(_)
+    }
+
+    // Tail Call Optimisation (TCO)
+    if (isTail) {
+      chain += Jump(LabelArg(labelGenerator.getLabel(target))) // tail call
+    } else {
+      chain += assemblyIR.Call(LabelArg(labelGenerator.getLabel(target))) // regular call
+    }
+
+    if (args.size > argRegs.size) {
+      chain += stack.drop(args.size - argRegs.size)
+    }
+
+    chain
+  }
+
+  private def generateComparison(destX: Register, cond: Cond)(using
+      stack: Stack
+  ): Chain[AsmLine] = {
+    var chain = Chain.empty[AsmLine]
+
+    chain += Compare(destX, stack.head)
+    chain += Set(Register(B8, AX), cond)
+    chain ++= zeroRest(RAX, B8)
+    chain += stack.drop()
+    chain += stack.push(B8, RAX)
+
+    chain
+  }
+
+  private def funcPrologue()(using stack: Stack): Chain[AsmLine] = {
+    var chain = Chain.empty[AsmLine]
+    chain += stack.push(Q64, RBP)
+    chain += Move(RBP, Register(Q64, SP))
+    chain
+  }
+
+  private def funcEpilogue(): Chain[AsmLine] = {
+    var chain = Chain.empty[AsmLine]
+    chain += Move(Register(Q64, SP), RBP)
+    chain += Pop(RBP)
+    chain += assemblyIR.Return()
+    chain
+  }
+
+  private def stackAlign: AsmLine = And(Register(Q64, SP), ImmediateVal(-16))
+  private def zeroRest(dest: Dest, size: Size): Chain[AsmLine] = size match {
+    case Q64 | 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) {
+    private def escaped: String =
+      s.flatMap(c => escapedCharsMapping.getOrElse(c, c.toString))
+  }
+}
diff --git a/src/main/wacc/backend/assemblyIR.scala b/src/main/wacc/backend/assemblyIR.scala
index 323742b..fbf51f5 100644
--- a/src/main/wacc/backend/assemblyIR.scala
+++ b/src/main/wacc/backend/assemblyIR.scala
@@ -6,47 +6,114 @@ object assemblyIR {
   sealed trait Operand
   sealed trait Src extends Operand // mem location, register and imm value
   sealed trait Dest extends Operand // mem location and register
-  enum RegSize {
-    case R64
-    case E32
 
-    override def toString = this match {
-      case R64 => "r"
-      case E32 => "e"
+  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,
-      Puts,
       Fflush,
       Exit,
-      PrintF
+      PrintF,
+      Malloc,
+      Free
 
     private val plt = "@plt"
 
     override def toString = this match {
       case Scanf  => "scanf" + plt
-      case Puts   => "puts" + plt
       case Fflush => "fflush" + plt
       case Exit   => "exit" + plt
       case PrintF => "printf" + plt
+      case Malloc => "malloc" + plt
+      case Free   => "free" + plt
     }
   }
 
-  enum Register extends Dest with Src {
-    case Named(name: String, size: RegSize)
-    case Scratch(num: Int, size: RegSize)
-    override def toString = this match {
-      case Named(name, size)  => s"${size}${name.toLowerCase()}"
-      case Scratch(num, size) => s"r${num}${if (size == RegSize.E32) "d" else ""}"
-    }
+  case class MemLocation(pointer: Register, opSize: Size) extends Dest with Src {
+    override def toString =
+      opSize.toString + s"[$pointer]"
   }
-  case class MemLocation(pointer: Long | Register) extends Dest with Src {
-    override def toString = pointer match {
-      case hex: Long     => f"[0x$hex%X]"
-      case reg: Register => s"[$reg]"
+
+  // TODO to string is wacky
+  case class IndexAddress(
+      base: Register,
+      offset: Int | LabelArg,
+      indexReg: Register = Register(Size.Q64, RegName.AX),
+      scale: Int = 0
+  ) extends Dest
+      with Src {
+    override def toString = if (scale != 0) {
+      s"[$base + $indexReg * $scale + $offset]"
+    } else {
+      s"[$base + $offset]"
     }
   }
 
@@ -64,30 +131,42 @@ object assemblyIR {
   }
   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("mul", ops*)
-  case class Divide(op1: Src) extends Operation("div", op1)
+  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)
 
   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)
 
   // stack operations
   case class Push(op1: Src) extends Operation("push", op1)
   case class Pop(op1: Src) extends Operation("pop", op1)
-  case class Call(op1: CLibFunc) extends Operation("call", op1)
+  case class Call(op1: CLibFunc | LabelArg) extends Operation("call", op1)
 
   case class Move(op1: Dest, op2: Src) extends Operation("mov", op1, op2)
-  case class Load(op1: Register, op2: MemLocation) extends Operation("lea ", op1, op2)
+  case class Load(op1: Register, op2: MemLocation | IndexAddress)
+      extends Operation("lea ", op1, op2)
+  case class CDQ() extends Operation("cdq")
 
   case class Return() extends Operation("ret")
 
   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,
@@ -108,4 +187,30 @@ object assemblyIR {
       case Always       => "mp"
     }
   }
+
+  enum Directive extends AsmLine {
+    case IntelSyntax, RoData, Text
+    case Global(name: String)
+    case Int(value: scala.Int)
+    case Asciz(string: String)
+
+    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".int $value"
+      case Asciz(string) => s".asciz \"$string\""
+    }
+  }
+
+  enum PrintFormat {
+    case Int, Char, String
+
+    override def toString(): String = this match {
+      case Int    => "%d"
+      case Char   => "%c"
+      case String => "%s"
+    }
+  }
 }
diff --git a/src/main/wacc/backend/sizeExtensions.scala b/src/main/wacc/backend/sizeExtensions.scala
new file mode 100644
index 0000000..798e290
--- /dev/null
+++ b/src/main/wacc/backend/sizeExtensions.scala
@@ -0,0 +1,35 @@
+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), KnownType.Array(KnownType.Char)) =>
+        KnownType.Int.size.toInt + elems.size.toInt * KnownType.Char.size.toInt
+      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
+    }
+  }
+}
diff --git a/src/main/wacc/backend/writer.scala b/src/main/wacc/backend/writer.scala
index b798af3..3c8dcfd 100644
--- a/src/main/wacc/backend/writer.scala
+++ b/src/main/wacc/backend/writer.scala
@@ -1,11 +1,12 @@
 package wacc
 
 import java.io.PrintStream
+import cats.data.Chain
 
 object writer {
   import assemblyIR._
 
-  def writeTo(asmList: List[AsmLine], printStream: PrintStream): Unit = {
-    asmList.foreach(printStream.println)
+  def writeTo(asmList: Chain[AsmLine], printStream: PrintStream): Unit = {
+    asmList.iterator.foreach(printStream.println)
   }
 }
diff --git a/src/main/wacc/frontend/lexer.scala b/src/main/wacc/frontend/lexer.scala
index 2efe517..4cb51a8 100644
--- a/src/main/wacc/frontend/lexer.scala
+++ b/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(
diff --git a/src/main/wacc/frontend/microWacc.scala b/src/main/wacc/frontend/microWacc.scala
index b9f6635..e2c1bdc 100644
--- a/src/main/wacc/frontend/microWacc.scala
+++ b/src/main/wacc/frontend/microWacc.scala
@@ -1,7 +1,5 @@
 package wacc
 
-import cats.data.NonEmptyList
-
 object microWacc {
   import wacc.types._
 
@@ -19,9 +17,7 @@ object microWacc {
       extends Expr(identTy)
       with CallTarget(identTy)
       with LValue
-  case class ArrayElem(value: LValue, indices: NonEmptyList[Expr])(ty: SemType)
-      extends Expr(ty)
-      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)
@@ -69,13 +65,16 @@ object microWacc {
   // Statements
   sealed trait Stmt
 
+  case class Builtin(val name: String)(retTy: SemType) extends CallTarget(retTy) {
+    override def toString(): String = name
+  }
   object Builtin {
-    case object ReadInt extends CallTarget(KnownType.Int)
-    case object ReadChar extends CallTarget(KnownType.Char)
-    case object Print extends CallTarget(?)
-    case object Println extends CallTarget(?)
-    case object Exit extends CallTarget(?)
-    case object Free extends CallTarget(?)
+    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) extends Stmt
diff --git a/src/main/wacc/frontend/typeChecker.scala b/src/main/wacc/frontend/typeChecker.scala
index e3960cb..002876d 100644
--- a/src/main/wacc/frontend/typeChecker.scala
+++ b/src/main/wacc/frontend/typeChecker.scala
@@ -110,7 +110,7 @@ object typeChecker {
         microWacc.FuncDecl(
           microWacc.Ident(name.v, name.uid)(retType),
           params.zip(paramTypes).map { case (ast.Param(_, ident), ty) =>
-            microWacc.Ident(ident.v, name.uid)(ty)
+            microWacc.Ident(ident.v, ident.uid)(ty)
           },
           stmts.toList
             .flatMap(
@@ -177,12 +177,14 @@ object typeChecker {
         microWacc.Assign(
           destTyped,
           microWacc.Call(
-            destTy match {
-              case KnownType.Int  => microWacc.Builtin.ReadInt
-              case KnownType.Char => microWacc.Builtin.ReadChar
-              case _              => microWacc.Builtin.ReadInt // we'll stop due to error anyway
-            },
-            Nil
+            microWacc.Builtin.Read,
+            List(
+              destTy match {
+                case KnownType.Int      => "%d".toMicroWaccCharArray
+                case KnownType.Char | _ => "%c".toMicroWaccCharArray
+              },
+              destTyped
+            )
           )
         )
       )
@@ -213,12 +215,38 @@ object typeChecker {
       )
     case ast.Print(expr, newline) =>
       // This constraint should never fail, the scope-checker should have caught it already
-      List(
-        microWacc.Call(
-          if newline then microWacc.Builtin.Println else microWacc.Builtin.Print,
-          List(checkValue(expr, Constraint.Unconstrained))
+      val exprTyped = 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) =>
+        List(
+          microWacc.Call(
+            func,
+            List(
+              s"$exprFormat${if newline then "\n" else ""}".toMicroWaccCharArray,
+              value
+            )
+          )
         )
-      )
+      }
+      exprTyped.ty match {
+        case KnownType.Bool =>
+          List(
+            microWacc.If(
+              exprTyped,
+              printfCall(microWacc.Builtin.Printf, "true".toMicroWaccCharArray),
+              printfCall(microWacc.Builtin.Printf, "false".toMicroWaccCharArray)
+            )
+          )
+        case KnownType.Array(KnownType.Char) =>
+          printfCall(microWacc.Builtin.PrintCharArray, exprTyped)
+        case _ => printfCall(microWacc.Builtin.Printf, exprTyped)
+      }
     case ast.If(cond, thenStmt, elseStmt) =>
       List(
         microWacc.If(
@@ -262,7 +290,7 @@ object typeChecker {
       microWacc.CharLiter(v)
     case l @ ast.StrLiter(v) =>
       KnownType.String.satisfies(constraint, l.pos)
-      microWacc.ArrayLiter(v.map(microWacc.CharLiter(_)).toList)(KnownType.String)
+      v.toMicroWaccCharArray
     case l @ ast.PairLiter() =>
       microWacc.NullLiter()(KnownType.Pair(?, ?).satisfies(constraint, l.pos))
     case ast.Parens(expr) => checkValue(expr, constraint)
@@ -410,10 +438,15 @@ object typeChecker {
         }
         (next, idxTyped)
       }
-      microWacc.ArrayElem(
+      val firstArrayElem = microWacc.ArrayElem(
         microWacc.Ident(id.v, id.uid)(arrayTy),
-        indicesTyped
+        indicesTyped.head
       )(elemTy.satisfies(constraint, value.pos))
+      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
+      microWacc.ArrayElem(arrayElem.value, arrayElem.index)(elemTy.satisfies(constraint, value.pos))
     case ast.Fst(elem) =>
       val elemTyped = checkLValue(
         elem,
@@ -421,7 +454,7 @@ object typeChecker {
       )
       microWacc.ArrayElem(
         elemTyped,
-        NonEmptyList.of(microWacc.IntLiter(0))
+        microWacc.IntLiter(0)
       )(elemTyped.ty match {
         case KnownType.Pair(left, _) =>
           left.satisfies(constraint, elem.pos)
@@ -434,11 +467,16 @@ object typeChecker {
       )
       microWacc.ArrayElem(
         elemTyped,
-        NonEmptyList.of(microWacc.IntLiter(1))
+        microWacc.IntLiter(1)
       )(elemTyped.ty match {
         case KnownType.Pair(_, right) =>
           right.satisfies(constraint, elem.pos)
         case _ => ctx.error(Error.InternalError(elem.pos, "snd must be applied to a pair"))
       })
   }
+
+  extension (s: String) {
+    def toMicroWaccCharArray: microWacc.ArrayLiter =
+      microWacc.ArrayLiter(s.map(microWacc.CharLiter(_)).toList)(KnownType.String)
+  }
 }
diff --git a/src/test/wacc/examples.scala b/src/test/wacc/examples.scala
index abff693..7c895ab 100644
--- a/src/test/wacc/examples.scala
+++ b/src/test/wacc/examples.scala
@@ -1,13 +1,14 @@
 package wacc
 
-import org.scalatest.{ParallelTestExecution, BeforeAndAfterAll}
+import org.scalatest.BeforeAndAfterAll
 import org.scalatest.flatspec.AnyFlatSpec
 import org.scalatest.Inspectors.forEvery
 import java.io.File
 import sys.process._
 import java.io.PrintStream
+import scala.io.Source
 
-class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll with ParallelTestExecution {
+class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll {
   val files =
     allWaccFiles("wacc-examples/valid").map { p =>
       (p.toString, List(0))
@@ -26,19 +27,38 @@ class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll with Paral
   forEvery(files) { (filename, expectedResult) =>
     val baseFilename = filename.stripSuffix(".wacc")
     given stdout: PrintStream = PrintStream(File(baseFilename + ".out"))
-    val result = compile(filename)
 
     s"$filename" should "be compiled with correct result" in {
+      val result = compile(filename)
       assert(expectedResult.contains(result))
     }
 
-    if (result == 0) it should "run with correct result" in {
+    if (expectedResult == List(0)) it should "run with correct result" in {
       if (fileIsDisallowedBackend(filename)) pending
 
       // Retrieve contents to get input and expected output + exit code
       val contents = scala.io.Source.fromFile(File(filename)).getLines.toList
       val inputLine =
-        contents.find(_.matches("^# ?[Ii]nput:.*$")).map(_.split(":").last.strip).getOrElse("")
+        contents
+          .find(_.matches("^# ?[Ii]nput:.*$"))
+          .map(line =>
+            ("" :: line.split(":").last.strip.split(" ").toList)
+              .sliding(2)
+              .flatMap { arr =>
+                if (
+                    // First entry has no space in front
+                    arr(0) == "" ||
+                      // int followed by non-digit, space can be removed
+                      arr(0).toIntOption.nonEmpty && !arr(1)(0).isDigit ||
+                      // non-int followed by int, space can be removed
+                      !arr(0).last.isDigit && arr(1).toIntOption.nonEmpty
+                  )
+                then List(arr(1))
+                else List(" ", arr(1))
+              }
+              .mkString
+          )
+          .getOrElse("")
       val outputLineIdx = contents.indexWhere(_.matches("^# ?[Oo]utput:.*$"))
       val expectedOutput =
         if (outputLineIdx == -1) ""
@@ -62,12 +82,17 @@ class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll with Paral
 
       // Run the executable with the provided input
       val stdout = new StringBuilder
-      // val execResult = s"$execFilename".!(ProcessLogger(stdout.append(_)))
-      val execResult =
-        s"echo $inputLine" #| s"timeout 5s $execFilename" ! ProcessLogger(stdout.append(_))
+      val process = s"timeout 5s $execFilename" run ProcessIO(
+        in = w => {
+          w.write(inputLine.getBytes)
+          w.close()
+        },
+        out = Source.fromInputStream(_).addString(stdout),
+        err = _ => ()
+      )
 
-      assert(execResult == expectedExit)
-      assert(stdout.toString == expectedOutput)
+      assert(process.exitValue == expectedExit)
+      assert(stdout.toString.replaceAll("0x[0-9a-f]+", "#addrs#") == expectedOutput)
     }
   }
 
@@ -80,22 +105,23 @@ class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll with Paral
       // format: off
       // disable formatting to avoid binPack
       "^.*wacc-examples/valid/advanced.*$",
-      "^.*wacc-examples/valid/array.*$",
-      "^.*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(?!echoInt\\.wacc).*$",
-      "^.*wacc-examples/valid/IO/IOLoop.wacc.*$",
-      "^.*wacc-examples/valid/IO/IOSequence.wacc.*$",
-      "^.*wacc-examples/valid/pairs.*$",
+      // "^.*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.*$",
+      // "^.*wacc-examples/valid/scope.*$",
+      // "^.*wacc-examples/valid/sequence.*$",
+      // "^.*wacc-examples/valid/variables.*$",
+      // "^.*wacc-examples/valid/while.*$",
       // format: on
     ).find(filename.matches).isDefined
 }
diff --git a/src/test/wacc/instructionSpec.scala b/src/test/wacc/instructionSpec.scala
index 6d427a5..feef0d4 100644
--- a/src/test/wacc/instructionSpec.scala
+++ b/src/test/wacc/instructionSpec.scala
@@ -1,42 +1,38 @@
 import org.scalatest.funsuite.AnyFunSuite
 import wacc.assemblyIR._
+import wacc.assemblyIR.Size._
+import wacc.assemblyIR.RegName._
 
 class instructionSpec extends AnyFunSuite {
 
-  val named64BitRegister = Register.Named("ax", RegSize.R64)
+  val named64BitRegister = Register(Q64, AX)
 
   test("named 64-bit register toString") {
     assert(named64BitRegister.toString == "rax")
   }
 
-  val named32BitRegister = Register.Named("ax", RegSize.E32)
+  val named32BitRegister = Register(D32, AX)
 
   test("named 32-bit register toString") {
     assert(named32BitRegister.toString == "eax")
   }
 
-  val scratch64BitRegister = Register.Scratch(1, RegSize.R64)
+  val scratch64BitRegister = Register(Q64, R8)
 
   test("scratch 64-bit register toString") {
-    assert(scratch64BitRegister.toString == "r1")
+    assert(scratch64BitRegister.toString == "r8")
   }
 
-  val scratch32BitRegister = Register.Scratch(1, RegSize.E32)
+  val scratch32BitRegister = Register(D32, R8)
 
   test("scratch 32-bit register toString") {
-    assert(scratch32BitRegister.toString == "r1d")
+    assert(scratch32BitRegister.toString == "r8d")
   }
 
-  val memLocationWithHex = MemLocation(0x12345678)
-
-  test("mem location with hex toString") {
-    assert(memLocationWithHex.toString == "[0x12345678]")
-  }
-
-  val memLocationWithRegister = MemLocation(named64BitRegister)
+  val memLocationWithRegister = MemLocation(named64BitRegister, Q64)
 
   test("mem location with register toString") {
-    assert(memLocationWithRegister.toString == "[rax]")
+    assert(memLocationWithRegister.toString == "qword ptr [rax]")
   }
 
   val immediateVal = ImmediateVal(123)
@@ -54,7 +50,7 @@ class instructionSpec extends AnyFunSuite {
   val subInstruction = Subtract(scratch64BitRegister, named64BitRegister)
 
   test("x86: sub instruction toString") {
-    assert(subInstruction.toString == "\tsub r1, rax")
+    assert(subInstruction.toString == "\tsub r8, rax")
   }
 
   val callInstruction = Call(CLibFunc.Scanf)