src/Typecheck.hs

@@ -37,14 +37,18 @@ typeCheckVariableDeclaration (VariableDeclaration dataType identifier maybeExpr)
         -- Type check the initializer expression if it exists
         checkedExpr = fmap (\expr -> typeCheckExpression expr symtab classes) maybeExpr
         exprType = fmap getTypeFromExpr checkedExpr
+        checkedExprWithType = case exprType of
+            Just "null" | isObjectType dataType -> Just (TypedExpression dataType NullLiteral)
+            _ -> checkedExpr
     in case (validType, redefined, exprType) of
         (False, _, _) -> error $ "Type '" ++ dataType ++ "' is not a valid type for variable '" ++ identifier ++ "'"
         (_, True, _) -> error $ "Variable '" ++ identifier ++ "' is redefined in the same scope"
         (_, _, Just t)
-            | t == "null" && isObjectType dataType -> VariableDeclaration dataType identifier checkedExpr
+            | t == "null" && isObjectType dataType -> VariableDeclaration dataType identifier checkedExprWithType
             | t /= dataType -> error $ "Type mismatch in declaration of '" ++ identifier ++ "': expected " ++ dataType ++ ", found " ++ t
-            | otherwise -> VariableDeclaration dataType identifier checkedExpr
+            | otherwise -> VariableDeclaration dataType identifier checkedExprWithType
-        (_, _, Nothing) -> VariableDeclaration dataType identifier checkedExpr
+        (_, _, Nothing) -> VariableDeclaration dataType identifier checkedExprWithType
+
 
 -- ********************************** Type Checking: Expressions **********************************
 
@@ -125,11 +129,14 @@ typeCheckStatementExpression (Assignment ref expr) symtab classes =
       ref' = typeCheckExpression ref symtab classes
       type' = getTypeFromExpr expr'
       type'' = getTypeFromExpr ref'
+      typeToAssign = if type' == "null" && isObjectType type'' then type'' else type'
+      exprWithType = if type' == "null" && isObjectType type'' then TypedExpression type'' NullLiteral else expr'
   in
-    if type'' == type' || (type' == "null" && isObjectType type'') then
+    if type'' == typeToAssign then
-      TypedStatementExpression type'' (Assignment ref' expr')
+      TypedStatementExpression type'' (Assignment ref' exprWithType)
     else
-      error $ "Type mismatch in assignment to variable: expected " ++ type'' ++ ", found " ++ type'
+      error $ "Type mismatch in assignment to variable: expected " ++ type'' ++ ", found " ++ typeToAssign
+
 
 typeCheckStatementExpression (ConstructorCall className args) symtab classes =
   case find (\(Class name _ _) -> name == className) classes of
@@ -168,25 +175,30 @@ typeCheckStatementExpression (MethodCall expr methodName args) symtab classes =
                 Just (Class _ methods _) ->
                     case find (\(MethodDeclaration retType name params _) -> name == methodName) methods of
                         Just (MethodDeclaration retType _ params _) ->
-                            let args' = map (\arg -> typeCheckExpression arg symtab classes) args
+                            let args' = zipWith
+                                    (\arg (ParameterDeclaration paramType _) ->
+                                        let argTyped = typeCheckExpression arg symtab classes
+                                        in if getTypeFromExpr argTyped == "null" && isObjectType paramType
+                                            then TypedExpression paramType NullLiteral
+                                            else argTyped
+                                    ) args params
                                 expectedTypes = [dataType | ParameterDeclaration dataType _ <- params]
                                 argTypes = map getTypeFromExpr args'
-                                typeMatches = zipWith (\expType argType -> (expType == argType || (argType == "null" && isObjectType expType), expType, argType)) expectedTypes argTypes
+                                typeMatches = zipWith
+                                    (\expType argType -> (expType == argType || (argType == "null" && isObjectType expType), expType, argType))
+                                    expectedTypes argTypes
                                 mismatches = filter (not . fst3) typeMatches
-                                    where fst3 (a, _, _) = a
+                                fst3 (a, _, _) = a
-                            in
+                            in if null mismatches && length args == length params
-                                if null mismatches && length args == length params then
+                                then TypedStatementExpression retType (MethodCall objExprTyped methodName args')
-                                    TypedStatementExpression retType (MethodCall objExprTyped methodName args')
+                                else if not (null mismatches)
-                                else if not (null mismatches) then
+                                    then error $ unlines $ ("Argument type mismatches for method '" ++ methodName ++ "':")
-                                    error $ unlines $ ("Argument type mismatches for method '" ++ methodName ++ "':")
                                         : [ "Expected: " ++ expType ++ ", Found: " ++ argType | (_, expType, argType) <- mismatches ]
-                                else
+                                    else error $ "Incorrect number of arguments for method '" ++ methodName ++ "'. Expected " ++ show (length expectedTypes) ++ ", found " ++ show (length args) ++ "."
-                                    error $ "Incorrect number of arguments for method '" ++ methodName ++ "'. Expected " ++ show (length expectedTypes) ++ ", found " ++ show (length args) ++ "."
                         Nothing -> error $ "Method '" ++ methodName ++ "' not found in class '" ++ objType ++ "'."
                 Nothing -> error $ "Class for object type '" ++ objType ++ "' not found."
         _ -> error "Invalid object type for method call. Object must have a class type."
-
+        
-
 typeCheckStatementExpression (PostIncrement expr) symtab classes =
   let expr' = typeCheckExpression expr symtab classes
       type' = getTypeFromExpr expr'
@@ -252,14 +264,18 @@ typeCheckStatement (LocalVariableDeclaration (VariableDeclaration dataType ident
         -- If there's an initializer expression, type check it
         let checkedExpr = fmap (\expr -> typeCheckExpression expr symtab classes) maybeExpr
             exprType = fmap getTypeFromExpr checkedExpr
+            checkedExprWithType = case (exprType, dataType) of
+                (Just "null", _) | isObjectType dataType -> Just (TypedExpression dataType NullLiteral)
+                _ -> checkedExpr
         in case exprType of
             Just t
                 | t == "null" && isObjectType dataType ->
-                    TypedStatement dataType (LocalVariableDeclaration (VariableDeclaration dataType identifier checkedExpr))
+                    TypedStatement dataType (LocalVariableDeclaration (VariableDeclaration dataType identifier checkedExprWithType))
                 | t /= dataType -> error $ "Type mismatch in declaration of '" ++ identifier ++ "': expected " ++ dataType ++ ", found " ++ t
-                | otherwise -> TypedStatement dataType (LocalVariableDeclaration (VariableDeclaration dataType identifier checkedExpr))
+                | otherwise -> TypedStatement dataType (LocalVariableDeclaration (VariableDeclaration dataType identifier checkedExprWithType))
             Nothing -> TypedStatement dataType (LocalVariableDeclaration (VariableDeclaration dataType identifier checkedExpr))
 
+
 typeCheckStatement (While cond stmt) symtab classes =
   let cond' = typeCheckExpression cond symtab classes
       stmt' =  typeCheckStatement stmt symtab classes
@@ -306,13 +322,17 @@ typeCheckStatement (Block statements) symtab classes =
 typeCheckStatement (Return expr) symtab classes =
   let methodReturnType = fromMaybe (error "Method return type not found in symbol table") (lookup "thisMeth" symtab)
       expr' = case expr of
-        Just e  -> Just (typeCheckExpression e symtab classes)
+        Just e  -> let eTyped = typeCheckExpression e symtab classes
+                   in if getTypeFromExpr eTyped == "null" && isObjectType methodReturnType 
+                      then Just (TypedExpression methodReturnType NullLiteral) 
+                      else Just eTyped
         Nothing -> Nothing
       returnType = maybe "void" getTypeFromExpr expr'
   in if returnType == methodReturnType || isSubtype returnType methodReturnType classes
        then TypedStatement returnType (Return expr')
        else error $ "Return: Return type mismatch: expected " ++ methodReturnType ++ ", found " ++ returnType
 
+
 typeCheckStatement (StatementExpressionStatement stmtExpr) symtab classes =
   let stmtExpr' = typeCheckStatementExpression stmtExpr symtab classes
    in TypedStatement (getTypeFromStmtExpr stmtExpr') (StatementExpressionStatement stmtExpr')