fix: put functions "(" within atomic

src/main/wacc/parser.scala

@@ -5,6 +5,7 @@ import parsley.Parsley
 import parsley.Parsley.{atomic, many, 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
 
@@ -75,15 +76,15 @@ object parser {
 
   // Statements
   private lazy val `<program>` = Program(
-    "begin" ~> many(`<func>`),
+    "begin" ~> many(atomic(`<type>` <~> `<ident>` <~ "(") <**> `<partial-func-decl>`),
     `<stmt>` <~ "end"
   )
-  private lazy val `<func>` = FuncDecl(
-    atomic(`<type>`),
-    atomic(`<ident>`) <~ "(",
-    sepBy(`<param>`, ",") <~ ")" <~ "is",
-    `<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>`, ";")
@@ -122,4 +123,14 @@ object parser {
   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
+    }
+  }
 }