Initial work on closures (again?)

src/backend/vm.nim

@@ -416,9 +416,11 @@ proc dispatch*(self: PeonVM) =
                 # variable
                 let idx = self.readLong().int
                 if idx > self.closedOver.high():
-                    self.closedOver.add(self.pop())
+                    # Note: we *peek* the stack, but we
+                    # don't pop!
+                    self.closedOver.add(self.peek())
                 else:
-                    self.closedOver[idx] = self.pop()
+                    self.closedOver[idx] = self.peek()
             of LoadClosure:
                 # Loads a closed-over variable onto the
                 # stack

src/config.nim

@@ -27,7 +27,7 @@ when len(PEON_COMMIT_HASH) != 40:
 const PEON_BRANCH* = "master"
 when len(PEON_BRANCH) > 255:
     {.fatal: "The git branch name's length must be less than or equal to 255 characters".}
-const DEBUG_TRACE_VM* = true # Traces VM execution
+const DEBUG_TRACE_VM* = false # Traces VM execution
 const DEBUG_TRACE_GC* = false # Traces the garbage collector (TODO)
 const DEBUG_TRACE_ALLOCATION* = false # Traces memory allocation/deallocation
 const DEBUG_TRACE_COMPILER* = false # Traces the compiler

src/frontend/compiler.nim

@@ -1499,8 +1499,11 @@ proc varDecl(self: Compiler, node: VarDecl) =
     let expected = self.inferType(node.valueType)
     let actual = self.inferType(node.value)
     if expected.isNil() and actual.isNil():
-        if node.value.kind == identExpr:
-            self.error(&"reference to undeclared identifier '{node.value.token.lexeme}'")
+        if node.value.kind == identExpr or node.value.kind == callExpr and CallExpr(node.value).callee.kind == identExpr:
+            var name = node.value.token.lexeme
+            if node.value.kind == callExpr:
+                name = CallExpr(node.value).callee.token.lexeme
+            self.error(&"reference to undeclared identifier '{name}'")
         self.error(&"'{node.name.token.lexeme}' has no type")
     elif not expected.isNil() and expected.kind == Mutable:  # I mean, variables *are* already mutable (some of them anyway)
         self.error(&"invalid type '{self.typeToStr(expected)}' for var")
@@ -1510,35 +1513,42 @@ proc varDecl(self: Compiler, node: VarDecl) =
     self.expression(node.value)
     self.declareName(node, mutable=node.token.kind == Var)
     self.emitByte(StoreVar)
-    self.emitBytes((self.names.high() + 1).toTriple())
+    self.emitBytes(self.names.len().toTriple())
 
 
 proc typeDecl(self: Compiler, node: TypeDecl) =
     ## Compiles type declarations
-    
+    # TODO
 
 
 proc funDecl(self: Compiler, node: FunDecl) =
     ## Compiles function declarations
-    # A function's code is just compiled linearly
-    # and then jumped over
+
     var function = self.currentFunction
     self.declareName(node)
     self.frames.add(self.names.high())
     let fn = self.names[^(node.arguments.len() + 1)]
+    # A function's code is just compiled linearly
+    # and then jumped over
     let jmp = self.emitJump(JumpForwards)
+    # Function's code starts after the jump
     fn.codePos = self.chunk.code.len()
     for argument in node.arguments:
+        # Pops off the operand stack onto the
+        # call stack
         self.emitByte(LoadArgument)
     if not node.returnType.isNil() and self.inferType(node.returnType).isNil():
+        # Are we returning a generic type?
         var isGeneric = false
         if node.returnType.kind == identExpr:
             let name = IdentExpr(node.returnType)
             for g in node.generics:
                 if name == g.name:
+                    # Yep!
                     isGeneric = true
                     break
         if not isGeneric:
+            # Nope
             self.error(&"cannot infer the type of '{node.returnType.token.lexeme}'")
     # TODO: Forward declarations
     if not node.body.isNil():
@@ -1589,6 +1599,7 @@ proc funDecl(self: Compiler, node: FunDecl) =
         self.endFunctionBeforeReturn()
         hasVal = hasVal and not typ.returnType.isNil()
         self.endScope(deleteNames=true, fromFunc=true)
+        # Terminates the function's context
         self.emitByte(OpCode.Return)
         if hasVal:
             self.emitByte(1)

src/frontend/meta/bytecode.nim

@@ -125,10 +125,10 @@ type
         ## Misc
         Assert, # Raises an AssertionFailed exception if x is false
         NoOp, # Just a no-op
-        LoadArgument,
-        LoadFunctionObj,
-        PopC,
-        PushC
+        LoadArgument,   # The caller uses this to pop off the argument from the operand stack onto the call stack
+        LoadFunctionObj,  # Creates and pushes a function object onto the stack with ip X
+        PopC,    # Pop off the call stack onto the operand stack
+        PushC    # Pop off the operand stack onto the call stack
 
 
 # We group instructions by their operation/operand types for easier handling when debugging

tests/closures.pn

@@ -1,9 +1,10 @@
-fn outer {
-   var x = 5;
-   fn inner {
-       var y = x;
+fn makeClosure(n: int): fn: int {
+   var x = n;
+   fn inner: int {
+       return x;
    }
-   inner();
+   return inner;
 }
 
-outer();
+
+makeClosure(1)();