diff --git a/.scalafmt.conf b/.scalafmt.conf
index c8ba10c..3df68b5 100644
--- a/.scalafmt.conf
+++ b/.scalafmt.conf
@@ -2,4 +2,5 @@ version = 3.8.6
 runner.dialect = scala3
 
 binPack.literalsExclude = []
+indent.infix.excludeRegex = "^$"
 maxColumn = 100
diff --git a/src/main/wacc/Main.scala b/src/main/wacc/Main.scala
index 1aa3eb3..9c59215 100644
--- a/src/main/wacc/Main.scala
+++ b/src/main/wacc/Main.scala
@@ -1,5 +1,6 @@
 package wacc
 
+import parsley.{Failure, Success}
 import scopt.OParser
 import java.io.File
 
@@ -28,6 +29,13 @@ val cliParser = {
   )
 }
 
+def compile(contents: String): Int = {
+  parser.parse(contents) match {
+    case Success(x)   => 0
+    case Failure(msg) => 100
+  }
+}
+
 def main(args: Array[String]): Unit =
   OParser.parse(cliParser, args, CliConfig()) match {
     case Some(config) =>
diff --git a/src/main/wacc/lexer.scala b/src/main/wacc/lexer.scala
index 4351294..094ac12 100644
--- a/src/main/wacc/lexer.scala
+++ b/src/main/wacc/lexer.scala
@@ -1,6 +1,7 @@
 package wacc
 
 import parsley.Parsley
+import parsley.character
 import parsley.token.{Basic, Lexer}
 import parsley.token.descriptions.*
 
@@ -45,6 +46,7 @@ object lexer {
   private val lexer = Lexer(desc)
   val ident = lexer.lexeme.names.identifier
   val integer = lexer.lexeme.integer.decimal32[Int]
+  val negateCheck = lexer.nonlexeme.symbol("-") ~> character.digit
   val charLit = lexer.lexeme.character.ascii
   val stringLit = lexer.lexeme.string.ascii
   val implicits = lexer.lexeme.symbol.implicits
diff --git a/src/main/wacc/parser.scala b/src/main/wacc/parser.scala
index 871ade0..84ee093 100644
--- a/src/main/wacc/parser.scala
+++ b/src/main/wacc/parser.scala
@@ -1,8 +1,136 @@
 package wacc
 
 import parsley.Result
+import parsley.Parsley
+import parsley.Parsley.{atomic, many, notFollowedBy, pure}
+import parsley.combinator.{countSome, sepBy}
+import parsley.expr.{precedence, SOps, InfixL, InfixN, InfixR, Prefix, Atoms}
+import parsley.errors.combinator._
+import parsley.cats.combinator.{sepBy1, some}
+import cats.data.NonEmptyList
 
 object parser {
-  def parse(input: String): Result[String, BigInt] = parser.parse(input)
-  private val parser = lexer.fully(???)
+  import lexer.implicits.implicitSymbol
+  import lexer.{ident, integer, charLit, stringLit, negateCheck}
+  import ast._
+
+  def parse(input: String): Result[String, Program] = parser.parse(input)
+  private val parser = lexer.fully(`<program>`)
+
+  // Expressions
+  private lazy val `<expr>`: Parsley[Expr] = precedence {
+    SOps(InfixR)(Or from "||") +:
+      SOps(InfixR)(And from "&&") +:
+      SOps(InfixN)(Eq from "==", Neq from "!=") +:
+      SOps(InfixN)(
+        Less from "<",
+        LessEq from "<=",
+        Greater from ">",
+        GreaterEq from ">="
+      ) +:
+      SOps(InfixL)(Add from "+", Sub from "-") +:
+      SOps(InfixL)(Mul from "*", Div from "/", Mod from "%") +:
+      SOps(Prefix)(
+        Not from "!",
+        Negate from (notFollowedBy(negateCheck) ~> "-"),
+        Len from "len",
+        Ord from "ord",
+        Chr from "chr"
+      ) +:
+      `<atom>`
+  }
+
+  // Atoms
+  private lazy val `<atom>`: Atoms[Expr6] = Atoms(
+    IntLiter(integer),
+    BoolLiter(("true" as true) | ("false" as false)),
+    CharLiter(charLit),
+    StrLiter(stringLit),
+    PairLiter from "null",
+    `<ident-or-array-elem>`,
+    Parens("(" ~> `<expr>` <~ ")")
+  )
+  private val `<ident>` = Ident(ident)
+  private lazy val `<ident-or-array-elem>` =
+    `<ident>` <**> (`<array-indices>` </> identity)
+  private val `<array-indices>` =
+    some("[" ~> `<expr>` <~ "]") map { indices =>
+      ArrayElem((_: Ident), indices)
+    }
+
+  // Types
+  private lazy val `<type>`: Parsley[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>` =
+    countSome("[" ~> "]") map { cnt => ArrayType((_: Type), cnt) }
+  private val `<pair-type>` = "pair"
+  private val `<pair-elems-type>`: Parsley[PairType] = PairType(
+    "(" ~> `<pair-elem-type>` <~ ",",
+    `<pair-elem-type>` <~ ")"
+  )
+  private lazy val `<pair-elem-type>` =
+    (`<base-type>` <**> (`<array-type>` </> identity)) |
+      `<pair-type>` ~> ((`<pair-elems-type>` <**> `<array-type>`) </> UntypedPairType)
+
+  // Statements
+  private lazy val `<program>` = Program(
+    "begin" ~> many(atomic(`<type>` <~> `<ident>` <~ "(") <**> `<partial-func-decl>`),
+    `<stmt>` <~ "end"
+  )
+  private lazy val `<partial-func-decl>` =
+    (sepBy(`<param>`, ",") <~ ")" <~ "is" <~> `<stmt>`.guardAgainst {
+      case stmts if !stmts.isReturning => Seq("All functions must end in a returning statement")
+    } <~ "end") map { (params, stmt) =>
+      (FuncDecl((_: Type), (_: Ident), params, stmt)).tupled
+    }
+  private lazy val `<param>` = Param(`<type>`, `<ident>`)
+  private lazy val `<stmt>`: Parsley[NonEmptyList[Stmt]] =
+    sepBy1(`<basic-stmt>`, ";")
+  private lazy val `<basic-stmt>` =
+    (Skip from "skip")
+      | Read("read" ~> `<lvalue>`)
+      | Free("free" ~> `<expr>`)
+      | Return("return" ~> `<expr>`)
+      | Exit("exit" ~> `<expr>`)
+      | Print("print" ~> `<expr>`, pure(false))
+      | Print("println" ~> `<expr>`, pure(true))
+      | If(
+        "if" ~> `<expr>` <~ "then",
+        `<stmt>` <~ "else",
+        `<stmt>` <~ "fi"
+      )
+      | While("while" ~> `<expr>` <~ "do", `<stmt>` <~ "done")
+      | Block("begin" ~> `<stmt>` <~ "end")
+      | VarDecl(`<type>`, `<ident>` <~ "=", `<rvalue>`)
+      | Assign(`<lvalue>` <~ "=", `<rvalue>`)
+  private lazy val `<lvalue>`: Parsley[LValue] =
+    `<pair-elem>` | `<ident-or-array-elem>`
+  private lazy val `<rvalue>`: Parsley[RValue] =
+    `<array-liter>` |
+      NewPair(
+        "newpair" ~> "(" ~> `<expr>` <~ ",",
+        `<expr>` <~ ")"
+      ) |
+      `<pair-elem>` |
+      Call(
+        "call" ~> `<ident>` <~ "(",
+        sepBy(`<expr>`, ",") <~ ")"
+      ) | `<expr>`
+  private lazy val `<pair-elem>` =
+    Fst("fst" ~> `<lvalue>`) | Snd("snd" ~> `<lvalue>`)
+  private lazy val `<array-liter>` = ArrayLiter(
+    "[" ~> sepBy(`<expr>`, ",") <~ "]"
+  )
+
+  extension (stmts: NonEmptyList[Stmt]) {
+    def isReturning: Boolean = stmts.last match {
+      case Return(_) | Exit(_)       => true
+      case If(_, thenStmt, elseStmt) => thenStmt.isReturning && elseStmt.isReturning
+      case While(_, body)            => body.isReturning
+      case Block(body)               => body.isReturning
+      case _                         => false
+    }
+  }
 }
diff --git a/src/test/wacc/examples.scala b/src/test/wacc/examples.scala
index 65aa54b..8d2b55e 100644
--- a/src/test/wacc/examples.scala
+++ b/src/test/wacc/examples.scala
@@ -3,7 +3,6 @@ package wacc
 import org.scalatest.{ParallelTestExecution, BeforeAndAfterAll}
 import org.scalatest.flatspec.AnyFlatSpec
 import org.scalatest.Inspectors.forEvery
-import parsley.{Success, Failure}
 
 class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll with ParallelTestExecution {
   val files =
@@ -26,10 +25,7 @@ class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll with Paral
   }) { (filename, expectedResult) =>
     s"$filename" should "be parsed with correct result" in {
       val contents = os.read(os.Path(filename))
-      parser.parse(contents) match {
-        case Success(x)   => assert(expectedResult.contains(x))
-        case Failure(msg) => fail(msg)
-      }
+      assert(expectedResult.contains(compile(contents)))
     }
   }
 
@@ -41,36 +37,36 @@ class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll with Paral
     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",
+      // "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",
+      // "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",
@@ -88,5 +84,6 @@ class ParallelExamplesSpec extends AnyFlatSpec with BeforeAndAfterAll with Paral
       // invalid (whack)
       "wacc-examples/invalid/whack"
       // format: on
+      // format: on
     ).find(filename.contains).isDefined
 }