Merge pull request 'bytecode' (#6) from bytecode into master

Reviewed-on: #6

Test/JavaSources/Main.java

@@ -1,7 +1,7 @@
 // compile all test files using:
 // ls Test/JavaSources/*.java | grep -v ".*Main.java" | xargs -I {} cabal run compiler {}
 // compile (in project root) using:
-// javac -g:none -sourcepath Test/JavaSources/ Test/JavaSources/Main.java 
+// pushd Test/JavaSources; javac -g:none Main.java; popd
 // afterwards, run using
 // java -ea -cp Test/JavaSources/ Main
 
@@ -11,6 +11,7 @@ public class Main {
         TestEmpty empty = new TestEmpty();
         TestFields fields = new TestFields();
         TestConstructor constructor = new TestConstructor(42);
+        TestArithmetic arithmetic = new TestArithmetic();
         TestMultipleClasses multipleClasses = new TestMultipleClasses();
         TestRecursion recursion = new TestRecursion(10);
         TestMalicious malicious = new TestMalicious();
@@ -21,6 +22,10 @@ public class Main {
         assert fields.a == 0 && fields.b == 42;
         // constructor parameters override initializers
         assert constructor.a == 42;
+        // basic arithmetics
+        assert arithmetic.basic(1, 2, 3) == 2;
+        // we have boolean logic as well
+        assert arithmetic.logic(false, false, true) == true;
         // multiple classes within one file work. Referencing another classes fields/methods works.
         assert multipleClasses.a.a == 42;
         // self-referencing classes work.

Test/JavaSources/TestArithmetic.java

@@ -0,0 +1,11 @@
+public class TestArithmetic {
+    public int basic(int a, int b, int c)
+    {
+        return a + b - c * a / b % c;
+    }
+
+    public boolean logic(boolean a, boolean b, boolean c)
+    {
+        return !a && (c || b);
+    }
+}

Test/JavaSources/TestRecursion.java

@@ -24,4 +24,11 @@ public class TestRecursion {
             return fibonacci(n - 1) + this.fibonacci(n - 2);
         }
     }
+
+    public int ackermann(int m, int n)
+    {
+        if (m == 0) return n + 1;
+        if (n == 0) return ackermann(m - 1, 1);
+        return ackermann(m - 1, ackermann(m, n - 1));
+    }
 }

doc/bytecode.md

@@ -4,20 +4,7 @@ Die Bytecodegenerierung ist letztendlich eine zweistufige Transformation:
 
 `Getypter AST -> [ClassFile] -> [[Word8]]`
 
-Vom AST, der bereits den Typcheck durchlaufen hat, wird zunächst eine Abbildung in die einzelnen ClassFiles vorgenommen. Diese ClassFiles werden anschließend in deren Byte-Repräsentation serialisiert.
+Vom AST, der bereits den Typcheck durchlaufen hat, wird zunächst eine Abbildung in die einzelnen ClassFiles vorgenommen. Diese ClassFiles werden anschließend in deren Byte-Repräsentation serialisiert. Dieser Teil der Aufgabenstellung wurde gemeinsam von Christian Brier und Matthias Raba umgesetzt.
-
-## Serialisierung
-
-Damit Bytecode generiert werden kann, braucht es Strukturen, die die Daten halten, die letztendlich serialisiert werden. Die JVM erwartet den kompilierten Code in handliche Pakete verpackt. Die Struktur dieser Pakete ist [so definiert](https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html).
-
-Jede Struktur, die in dieser übergreifenden Class File vorkommt, haben wir in Haskell abgebildet. Es gibt z.B die Struktur "ClassFile", die wiederum weitere Strukturen wie z.B Informationen über Felder oder Methoden der Klasse. Alle diese Strukturen implementieren folgendes TypeClass:
-
-```
-class Serializable a where
-    serialize :: a -> [Word8]
-```
-
-Die Struktur ClassFile ruft für deren Kinder rekursiv diese `serialize` Funktion auf. Am Ende bleibt eine flache Word8-Liste übrig, die Serialisierung ist damit abgeschlossen.
 
 ## Codegenerierung
 
@@ -32,7 +19,6 @@ Die Idee hinter beiden ist, dass sie jeweils zwei Inputs haben, wobei der Rückg
 Der Nutzer ruft beispielsweise die Funktion `classBuilder` auf. Diese wendet nach und nach folgende Transformationen an:
 
 ```
-
         methodsWithInjectedConstructor = injectDefaultConstructor methods
         methodsWithInjectedInitializers = injectFieldInitializers name fields methodsWithInjectedConstructor
 
@@ -47,7 +33,7 @@ Zuerst wird (falls notwendig) ein leerer Defaultkonstruktor in die Classfile ein
     2. Hinzufügen aller Methoden (nur Prototypen)
     3. Hinzufügen des Bytecodes in allen Methoden
 
-Die Unterteilung von Schritt 2 und 3 ist deswegen notwendig, weil der Code einer Methode auch eine andere, erst nachher deklarierte Methode aufrufen kann. Nach Schritt 2 sind alle Methoden der Klasse bekannt. Wie beschrieben wird auch hier der Zustand über alle Faltungen mitgenommen. Jeder Schritt hat Zugriff auf alle Daten, die aus dem vorherigen Schritt bleiben. Sukkzessive wird eine korrekte ClassFile aufgebaut.
+Die Unterteilung von Schritt 2 und 3 ist deswegen notwendig, weil der Code einer Methode auch eine andere, erst nachher deklarierte Methode aufrufen kann. Nach Schritt 2 sind alle Methoden der Klasse bekannt. Wie beschrieben wird auch hier der Zustand über alle Faltungen mitgenommen. Jeder Schritt hat Zugriff auf alle Daten, die aus dem vorherigen Schritt bleiben. Sukzessive wird eine korrekte ClassFile aufgebaut.
 
 Besonders interessant ist hierbei Schritt 3. Dort wird das Verhalten jeder einzelnen Methode in Bytecode übersetzt. In diesem Schritt werden zusätzlich zu den `Buildern` noch die `Assembler` verwendet (Definition siehe oben.) Die Assembler funktionieren ähnlich wie die Builder, arbeiten allerdings nicht auf einer ClassFile, sondern auf dem Inhalt einer Methode: Sie verarbeiten jeweils ein Tupel:
 
@@ -67,3 +53,27 @@ assembleExpression (constants, ops, lvars) (TypedExpression _ NullLiteral) =
 Hier werden die Konstanten und lokalen Variablen des Inputs nicht berührt, dem Bytecode wird lediglich die Operation `aconst_null` hinzugefügt. Damit ist das Verhalten des gematchten Inputs - eines Nullliterals - abgebildet.
 
 Die Assembler rufen sich teilweise rekursiv selbst auf, da ja auch der AST verschachteltes Verhalten abbilden kann. Der Startpunkt für die Assembly einer Methode ist der Builder `methodAssembler`. Dieser entspricht Schritt 3 in der obigen Übersicht.
+
+## Serialisierung
+
+Damit Bytecode generiert werden kann, braucht es Strukturen, die die Daten halten, die letztendlich serialisiert werden. Die JVM erwartet den kompilierten Code in handliche Pakete verpackt. Die Struktur dieser Pakete ist [so definiert](https://docs.oracle.com/javase/specs/jvms/se7/html/jvms-4.html).
+
+Jede Struktur, die in dieser übergreifenden Class File vorkommt, haben wir in Haskell abgebildet. Es gibt z.B die Struktur "ClassFile", die wiederum weitere Strukturen wie z.B Informationen über Felder oder Methoden der Klasse beinhaltet. Alle diese Strukturen implementieren folgende TypeClass:
+
+```
+class Serializable a where
+    serialize :: a -> [Word8]
+```
+
+Hier ist ein Beispiel anhand der Serialisierung der einzelnen Operationen:
+
+```
+instance Serializable Operation where
+    serialize Opiadd                    = [0x60]
+    serialize Opisub                    = [0x64]
+    serialize Opimul                    = [0x68]
+    ...
+    serialize (Opgetfield index)        = 0xB4 : unpackWord16 index
+```
+
+Die Struktur ClassFile ruft für deren Kinder rekursiv diese `serialize` Funktion auf und konkateniert die Ergebnisse. Am Ende bleibt eine flache Word8-Liste übrig, die Serialisierung ist damit abgeschlossen. Da der Typecheck sicherstellt, dass alle referenzierten Methoden/Felder gültig sind, kann die Übersetzung der einzelnen Klassen voneinander unabhängig geschehen.

src/ByteCode/Assembler.hs

@@ -12,12 +12,12 @@ type Assembler a = ([ConstantInfo], [Operation], [String]) -> a -> ([ConstantInf
 
 assembleExpression :: Assembler Expression
 assembleExpression (constants, ops, lvars) (TypedExpression _ (BinaryOperation op a b))
-    | elem op [Addition, Subtraction, Multiplication, Division, Modulo, BitwiseAnd, BitwiseOr, BitwiseXor, And, Or] = let
+    | op `elem` [Addition, Subtraction, Multiplication, Division, Modulo, BitwiseAnd, BitwiseOr, BitwiseXor, And, Or] = let
             (aConstants, aOps, _) = assembleExpression (constants, ops, lvars) a
             (bConstants, bOps, _) = assembleExpression (aConstants, aOps, lvars) b
         in
             (bConstants, bOps ++ [binaryOperation op], lvars)
-    | elem op [CompareEqual, CompareNotEqual, CompareLessThan, CompareLessOrEqual, CompareGreaterThan, CompareGreaterOrEqual] = let
+    | op `elem` [CompareEqual, CompareNotEqual, CompareLessThan, CompareLessOrEqual, CompareGreaterThan, CompareGreaterOrEqual] = let
             (aConstants, aOps, _) = assembleExpression (constants, ops, lvars) a
             (bConstants, bOps, _) = assembleExpression (aConstants, aOps, lvars) b
             cmp_op = comparisonOperation op 9
@@ -60,7 +60,7 @@ assembleExpression (constants, ops, lvars) (TypedExpression _ (UnaryOperation Mi
 assembleExpression (constants, ops, lvars) (TypedExpression dtype (LocalVariable name))
     | name == "this" = (constants, ops ++ [Opaload 0], lvars)
     | otherwise = let
-            localIndex = findIndex ((==) name) lvars
+            localIndex = elemIndex name lvars
             isPrimitive = elem dtype ["char", "boolean", "int"]
         in case localIndex of
             Just index -> (constants, ops ++ if isPrimitive then [Opiload (fromIntegral index)] else [Opaload (fromIntegral index)], lvars)
@@ -69,7 +69,7 @@ assembleExpression (constants, ops, lvars) (TypedExpression dtype (LocalVariable
 assembleExpression (constants, ops, lvars) (TypedExpression dtype (StatementExpressionExpression stmtexp)) =
         assembleStatementExpression (constants, ops, lvars) stmtexp
 
-assembleExpression _ expr = error ("unimplemented: " ++ show expr)
+assembleExpression _ expr = error ("Unknown expression: " ++ show expr)
 
 assembleNameChain :: Assembler Expression
 assembleNameChain input (TypedExpression _ (BinaryOperation NameResolution (TypedExpression atype a) (TypedExpression _ (FieldVariable _)))) =
@@ -84,7 +84,7 @@ assembleStatementExpression
         target = resolveNameChain (TypedExpression dtype receiver)
     in case target of
         (TypedExpression dtype (LocalVariable name)) -> let
-                localIndex = findIndex ((==) name) lvars
+                localIndex = elemIndex name lvars
                 (constants_a, ops_a, _) = assembleExpression (constants, ops, lvars) expr
                 isPrimitive = elem dtype ["char", "boolean", "int"]
             in case localIndex of
@@ -99,7 +99,7 @@ assembleStatementExpression
                         (constants_a, ops_a, _) = assembleExpression (constants_r, ops_r, lvars) expr
                     in
                         (constants_a, ops_a ++ [Opdup_x1, Opputfield (fromIntegral fieldIndex)], lvars)
-                something_else -> error ("expected TypedExpression, but got: " ++ show something_else)
+                something_else -> error ("Expected TypedExpression, but got: " ++ show something_else)
 
 assembleStatementExpression
     (constants, ops, lvars)
@@ -107,12 +107,12 @@ assembleStatementExpression
         target = resolveNameChain (TypedExpression dtype receiver)
     in case target of
         (TypedExpression dtype (LocalVariable name)) -> let
-                localIndex = findIndex ((==) name) lvars
+                localIndex = elemIndex name lvars
-                expr = (TypedExpression dtype (LocalVariable name))
+                expr = TypedExpression dtype (LocalVariable name)
                 (exprConstants, exprOps, _) = assembleExpression (constants, ops, lvars) expr
             in case localIndex of
                 Just index -> (exprConstants, exprOps ++ [Opsipush 1, Opiadd, Opdup, Opistore (fromIntegral index)], lvars)
-                Nothing -> error("No such local variable found in local variable pool: " ++ name)
+                Nothing -> error ("No such local variable found in local variable pool: " ++ name)
         (TypedExpression dtype (FieldVariable name)) -> let
                 owner = resolveNameChainOwner (TypedExpression dtype receiver)
             in case owner of
@@ -121,7 +121,7 @@ assembleStatementExpression
                         (constants_r, ops_r, _) = assembleNameChain (constants_f, ops, lvars) (TypedExpression dtype receiver)
                     in
                         (constants_r, ops_r ++ [Opdup, Opgetfield (fromIntegral fieldIndex), Opsipush 1, Opiadd, Opdup_x1, Opputfield (fromIntegral fieldIndex)], lvars)
-                something_else -> error ("expected TypedExpression, but got: " ++ show something_else)
+                something_else -> error ("Expected TypedExpression, but got: " ++ show something_else)
 
 assembleStatementExpression
     (constants, ops, lvars)
@@ -129,12 +129,12 @@ assembleStatementExpression
         target = resolveNameChain (TypedExpression dtype receiver)
     in case target of
         (TypedExpression dtype (LocalVariable name)) -> let
-                localIndex = findIndex ((==) name) lvars
+                localIndex = elemIndex name lvars
-                expr = (TypedExpression dtype (LocalVariable name))
+                expr = TypedExpression dtype (LocalVariable name)
                 (exprConstants, exprOps, _) = assembleExpression (constants, ops, lvars) expr
             in case localIndex of
                 Just index -> (exprConstants, exprOps ++ [Opsipush 1, Opisub, Opdup, Opistore (fromIntegral index)], lvars)
-                Nothing -> error("No such local variable found in local variable pool: " ++ name)
+                Nothing -> error ("No such local variable found in local variable pool: " ++ name)
         (TypedExpression dtype (FieldVariable name)) -> let
                 owner = resolveNameChainOwner (TypedExpression dtype receiver)
             in case owner of
@@ -143,7 +143,7 @@ assembleStatementExpression
                         (constants_r, ops_r, _) = assembleNameChain (constants_f, ops, lvars) (TypedExpression dtype receiver)
                     in
                         (constants_r, ops_r ++ [Opdup, Opgetfield (fromIntegral fieldIndex), Opsipush 1, Opisub, Opdup_x1, Opputfield (fromIntegral fieldIndex)], lvars)
-                something_else -> error ("expected TypedExpression, but got: " ++ show something_else)
+                something_else -> error ("Expected TypedExpression, but got: " ++ show something_else)
 
 assembleStatementExpression
     (constants, ops, lvars)
@@ -151,12 +151,12 @@ assembleStatementExpression
         target = resolveNameChain (TypedExpression dtype receiver)
     in case target of
         (TypedExpression dtype (LocalVariable name)) -> let
-                localIndex = findIndex ((==) name) lvars
+                localIndex = elemIndex name lvars
-                expr = (TypedExpression dtype (LocalVariable name))
+                expr = TypedExpression dtype (LocalVariable name)
                 (exprConstants, exprOps, _) = assembleExpression (constants, ops, lvars) expr
             in case localIndex of
                 Just index -> (exprConstants, exprOps ++ [Opdup, Opsipush 1, Opiadd, Opistore (fromIntegral index)], lvars)
-                Nothing -> error("No such local variable found in local variable pool: " ++ name)
+                Nothing -> error ("No such local variable found in local variable pool: " ++ name)
         (TypedExpression dtype (FieldVariable name)) -> let
                 owner = resolveNameChainOwner (TypedExpression dtype receiver)
             in case owner of
@@ -165,7 +165,7 @@ assembleStatementExpression
                         (constants_r, ops_r, _) = assembleNameChain (constants_f, ops, lvars) (TypedExpression dtype receiver)
                     in
                         (constants_r, ops_r ++ [Opdup, Opgetfield (fromIntegral fieldIndex), Opdup_x1, Opsipush 1, Opiadd, Opputfield (fromIntegral fieldIndex)], lvars)
-                something_else -> error ("expected TypedExpression, but got: " ++ show something_else)
+                something_else -> error ("Expected TypedExpression, but got: " ++ show something_else)
 
 assembleStatementExpression
     (constants, ops, lvars)
@@ -173,12 +173,12 @@ assembleStatementExpression
         target = resolveNameChain (TypedExpression dtype receiver)
     in case target of
         (TypedExpression dtype (LocalVariable name)) -> let
-                localIndex = findIndex ((==) name) lvars
+                localIndex = elemIndex name lvars
-                expr = (TypedExpression dtype (LocalVariable name))
+                expr = TypedExpression dtype (LocalVariable name)
                 (exprConstants, exprOps, _) = assembleExpression (constants, ops, lvars) expr
             in case localIndex of
                 Just index -> (exprConstants, exprOps ++ [Opdup, Opsipush 1, Opisub, Opistore (fromIntegral index)], lvars)
-                Nothing -> error("No such local variable found in local variable pool: " ++ name)
+                Nothing -> error ("No such local variable found in local variable pool: " ++ name)
         (TypedExpression dtype (FieldVariable name)) -> let
                 owner = resolveNameChainOwner (TypedExpression dtype receiver)
             in case owner of
@@ -187,7 +187,7 @@ assembleStatementExpression
                         (constants_r, ops_r, _) = assembleNameChain (constants_f, ops, lvars) (TypedExpression dtype receiver)
                     in
                         (constants_r, ops_r ++ [Opdup, Opgetfield (fromIntegral fieldIndex), Opdup_x1, Opsipush 1, Opisub, Opputfield (fromIntegral fieldIndex)], lvars)
-                something_else -> error ("expected TypedExpression, but got: " ++ show something_else)
+                something_else -> error ("Expected TypedExpression, but got: " ++ show something_else)
 
 assembleStatementExpression
     (constants, ops, lvars)
@@ -231,7 +231,7 @@ assembleStatement (constants, ops, lvars) (TypedStatement dtype (If expr if_stmt
         else_length = sum (map opcodeEncodingLength ops_elsea)
     in case dtype of
         "void" -> (constants_ifa, ops ++ ops_cmp ++ [Opsipush 0, Opif_icmpeq (if_length + 6)] ++ ops_ifa ++ [Opgoto (else_length + 3)] ++ ops_elsea, lvars)
-        otherwise -> (constants_ifa, ops ++ ops_cmp ++ [Opsipush 0, Opif_icmpeq (if_length + 3)] ++ ops_ifa ++ ops_elsea, lvars)
+        _ -> (constants_ifa, ops ++ ops_cmp ++ [Opsipush 0, Opif_icmpeq (if_length + 3)] ++ ops_ifa ++ ops_elsea, lvars)
 
 assembleStatement (constants, ops, lvars) (TypedStatement _ (While expr stmt)) = let
         (constants_cmp, ops_cmp, _) = assembleExpression (constants, [], lvars) expr
@@ -257,20 +257,19 @@ assembleStatement (constants, ops, lvars) (TypedStatement _ (StatementExpression
     in
         (constants_e, ops_e ++ [Oppop], lvars_e)
 
-assembleStatement _ stmt = error ("Not yet implemented: " ++ show stmt)
+assembleStatement _ stmt = error ("Unknown statement: " ++ show stmt)
 
 
 assembleMethod :: Assembler MethodDeclaration
 assembleMethod (constants, ops, lvars) (MethodDeclaration returntype name _ (TypedStatement _ (Block statements)))
     | name == "<init>"  = let
             (constants_a, ops_a, lvars_a) = foldl assembleStatement (constants, ops, lvars) statements
-            init_ops = [Opaload 0, Opinvokespecial 2]
         in
-            (constants_a, init_ops ++ ops_a ++ [Opreturn], lvars_a)
+            (constants_a, [Opaload 0, Opinvokespecial 2] ++ ops_a ++ [Opreturn], lvars_a)
     | otherwise = case returntype of
         "void" -> let
                 (constants_a, ops_a, lvars_a) = foldl assembleStatement (constants, ops, lvars) statements
             in
                 (constants_a, ops_a ++ [Opreturn], lvars_a)
-        otherwise -> foldl assembleStatement (constants, ops, lvars) statements
+        _ -> foldl assembleStatement (constants, ops, lvars) statements
 assembleMethod _ (MethodDeclaration _ _ _ stmt) = error ("Typed block expected for method body, got: " ++ show stmt)

src/ByteCode/Builder.hs

@@ -22,14 +22,14 @@ fieldBuilder (VariableDeclaration datatype name _) input = let
             ]
         field = MemberInfo {
             memberAccessFlags = accessPublic,
-            memberNameIndex = (fromIntegral (baseIndex + 2)),
+            memberNameIndex = fromIntegral (baseIndex + 2),
-            memberDescriptorIndex = (fromIntegral (baseIndex + 3)),
+            memberDescriptorIndex = fromIntegral (baseIndex + 3),
             memberAttributes = []
             }
     in
         input {
-            constantPool = (constantPool input) ++ constants,
+            constantPool = constantPool input ++ constants,
-            fields = (fields input) ++ [field]
+            fields = fields input ++ [field]
         }
 
 
@@ -46,18 +46,17 @@ methodBuilder (MethodDeclaration returntype name parameters statement) input = l
 
         method = MemberInfo {
             memberAccessFlags = accessPublic,
-            memberNameIndex = (fromIntegral (baseIndex + 2)),
+            memberNameIndex = fromIntegral (baseIndex + 2),
-            memberDescriptorIndex = (fromIntegral (baseIndex + 3)),
+            memberDescriptorIndex = fromIntegral (baseIndex + 3),
             memberAttributes = []
             }
     in
         input {
-            constantPool = (constantPool input) ++ constants,
+            constantPool = constantPool input ++ constants,
-            methods = (methods input) ++ [method]
+            methods = methods input ++ [method]
         }
 
 
-
 methodAssembler :: ClassFileBuilder MethodDeclaration
 methodAssembler (MethodDeclaration returntype name parameters statement) input = let
         methodConstantIndex = findMethodIndex input name
@@ -66,21 +65,22 @@ methodAssembler (MethodDeclaration returntype name parameters statement) input =
         Just index -> let
                 declaration = MethodDeclaration returntype name parameters statement
                 paramNames = "this" : [name | ParameterDeclaration _ name <- parameters]
-            in case (splitAt index (methods input)) of
+            in case splitAt index (methods input) of
                 (pre, []) -> input
                 (pre, method : post) -> let
-                        (_, bytecode, _) = assembleMethod (constantPool input, [], paramNames) declaration
+                        (constants, bytecode, aParamNames) = assembleMethod (constantPool input, [], paramNames) declaration
                         assembledMethod = method {
                             memberAttributes = [
                                 CodeAttribute {
-                                    attributeMaxStack = 420,
+                                    attributeMaxStack = fromIntegral $ maxStackDepth constants bytecode,
-                                    attributeMaxLocals = 420,
+                                    attributeMaxLocals = fromIntegral $ length aParamNames,
                                     attributeCode = bytecode
                                 }
                             ]
                         }
                     in
                         input {
+                            constantPool = constants,
                             methods = pre ++ (assembledMethod : post)
                         }
 
@@ -94,11 +94,12 @@ classBuilder (Class name methods fields) _ = let
             Utf8Info "java/lang/Object",
             Utf8Info "<init>",
             Utf8Info "()V",
-            Utf8Info "Code"
+            Utf8Info "Code",
+            ClassInfo 9,
+            Utf8Info name
             ]
-        nameConstants = [ClassInfo 9, Utf8Info name]
         nakedClassFile = ClassFile {
-            constantPool = baseConstants ++ nameConstants,
+            constantPool = baseConstants,
             accessFlags = accessPublic,
             thisClass = 8,
             superClass = 1,
@@ -107,9 +108,13 @@ classBuilder (Class name methods fields) _ = let
             attributes = []
         }
 
+        -- if a class has no constructor, inject an empty one.
         methodsWithInjectedConstructor = injectDefaultConstructor methods
+        -- for every constructor, prepend all initialization assignments for fields.
         methodsWithInjectedInitializers = injectFieldInitializers name fields methodsWithInjectedConstructor
 
+        -- add fields, then method bodies to the classfile. After all referable names are known,
+        -- assemble the methods into bytecode.
         classFileWithFields = foldr fieldBuilder nakedClassFile fields
         classFileWithMethods = foldr methodBuilder classFileWithFields methodsWithInjectedInitializers
         classFileWithAssembledMethods = foldr methodAssembler classFileWithMethods methodsWithInjectedInitializers

src/ByteCode/ClassFile.hs

@@ -1,14 +1,4 @@
-module ByteCode.ClassFile(
+module ByteCode.ClassFile where
-    ConstantInfo(..),
-    Attribute(..),
-    MemberInfo(..),
-    ClassFile(..),
-    Operation(..),
-    serialize,
-    emptyClassFile,
-    opcodeEncodingLength,
-    className
-) where
 
 import Data.Word
 import Data.Int
@@ -99,10 +89,10 @@ emptyClassFile = ClassFile {
 
 className :: ClassFile -> String
 className classFile = let
-        classInfo = (constantPool classFile)!!(fromIntegral (thisClass classFile))
+        classInfo = constantPool classFile !! fromIntegral (thisClass classFile)
     in case classInfo of
         Utf8Info className -> className
-        otherwise -> error ("expected Utf8Info but got: " ++ show otherwise)
+        unexpected_element -> error ("expected Utf8Info but got: " ++ show unexpected_element)
 
 
 opcodeEncodingLength :: Operation -> Word16
@@ -201,10 +191,10 @@ instance Serializable Attribute where
     serialize (CodeAttribute { attributeMaxStack = maxStack,
                                attributeMaxLocals = maxLocals,
                                attributeCode = code }) = let
-            assembledCode = concat (map serialize code)
+            assembledCode = concatMap serialize code
         in
             unpackWord16 7                                                  -- attribute_name_index
-            ++ unpackWord32 (12 + (fromIntegral (length assembledCode)))    -- attribute_length
+            ++ unpackWord32 (12 + fromIntegral (length assembledCode))      -- attribute_length
             ++ unpackWord16 maxStack                                        -- max_stack
             ++ unpackWord16 maxLocals                                       -- max_locals
             ++ unpackWord32 (fromIntegral (length assembledCode))           -- code_length

src/ByteCode/Util.hs

@@ -4,29 +4,28 @@ import Data.Int
 import Ast
 import ByteCode.ClassFile
 import Data.List
-import Data.Maybe (mapMaybe)
+import Data.Maybe (mapMaybe, isJust)
 import Data.Word (Word8, Word16, Word32)
 
 -- walks the name resolution chain. returns the innermost Just LocalVariable/FieldVariable or Nothing.
 resolveNameChain :: Expression -> Expression
 resolveNameChain (TypedExpression _ (BinaryOperation NameResolution a b)) = resolveNameChain b
-resolveNameChain (TypedExpression dtype (LocalVariable name)) = (TypedExpression dtype (LocalVariable name))
+resolveNameChain (TypedExpression dtype (LocalVariable name)) = TypedExpression dtype (LocalVariable name)
-resolveNameChain (TypedExpression dtype (FieldVariable name)) = (TypedExpression dtype (FieldVariable name))
+resolveNameChain (TypedExpression dtype (FieldVariable name)) = TypedExpression dtype (FieldVariable name)
-resolveNameChain invalidExpression = error ("expected a NameResolution or Local/Field Variable but got: " ++ show(invalidExpression))
+resolveNameChain invalidExpression = error ("expected a NameResolution or Local/Field Variable but got: " ++ show invalidExpression)
 
 -- walks the name resolution chain. returns the second-to-last item of the namechain.
 resolveNameChainOwner :: Expression -> Expression
 resolveNameChainOwner (TypedExpression _ (BinaryOperation NameResolution a (TypedExpression dtype (FieldVariable name)))) = a
 resolveNameChainOwner (TypedExpression _ (BinaryOperation NameResolution a b)) = resolveNameChain b
-resolveNameChainOwner invalidExpression = error ("expected a NameResolution or Local/Field Variable but got: " ++ show(invalidExpression))
+resolveNameChainOwner invalidExpression = error ("expected a NameResolution or Local/Field Variable but got: " ++ show invalidExpression)
-
 
 methodDescriptor :: MethodDeclaration -> String
 methodDescriptor (MethodDeclaration returntype _ parameters _) = let
         parameter_types = [datatype | ParameterDeclaration datatype _ <- parameters]
     in
         "("
-        ++ (concat (map datatypeDescriptor parameter_types))
+        ++ concatMap datatypeDescriptor parameter_types
         ++ ")"
         ++ datatypeDescriptor returntype
 
@@ -35,49 +34,69 @@ methodDescriptorFromParamlist parameters returntype = let
         parameter_types = [datatype | TypedExpression datatype _ <- parameters]
     in
         "("
-        ++ (concat (map datatypeDescriptor parameter_types))
+        ++ concatMap datatypeDescriptor parameter_types
         ++ ")"
         ++ datatypeDescriptor returntype
 
-memberInfoIsMethod :: [ConstantInfo] -> MemberInfo -> Bool
+-- recursively parses a given type signature into a list of parameter types and the method return type.
-memberInfoIsMethod constants info = elem '(' (memberInfoDescriptor constants info)
+-- As an initial parameter, you can supply ([], "void").
+parseMethodType :: ([String], String) -> String -> ([String], String)
+parseMethodType (params, returnType) ('(' : descriptor) = parseMethodType (params, returnType) descriptor
+parseMethodType (params, returnType) ('I' : descriptor) = parseMethodType (params ++ ["I"], returnType) descriptor
+parseMethodType (params, returnType) ('C' : descriptor) = parseMethodType (params ++ ["C"], returnType) descriptor
+parseMethodType (params, returnType) ('Z' : descriptor) = parseMethodType (params ++ ["Z"], returnType) descriptor
+parseMethodType (params, returnType) ('L' : descriptor) = let
+        typeLength = elemIndex ';' descriptor
+    in case typeLength of
+        Just length -> let
+                (typeName, semicolon : restOfDescriptor) = splitAt length descriptor
+            in
+                parseMethodType (params ++ [typeName], returnType) restOfDescriptor
+        Nothing -> error $ "unterminated class type in function signature: " ++ show descriptor
+parseMethodType (params, _) (')' : descriptor) = (params, descriptor)
+parseMethodType _ descriptor = error $ "expected start of type name (L, I, C, Z) but got: " ++ descriptor
 
+-- given a method index (constant pool index), 
+-- returns the full type of the method. (i.e (LSomething;II)V)
+methodTypeFromIndex :: [ConstantInfo] -> Int -> String
+methodTypeFromIndex constants index = case constants !! fromIntegral (index - 1) of
+    MethodRefInfo _ nameAndTypeIndex -> case constants !! fromIntegral (nameAndTypeIndex - 1) of
+        NameAndTypeInfo _ typeIndex -> case constants !! fromIntegral (typeIndex - 1) of
+            Utf8Info typeLiteral -> typeLiteral
+            unexpectedElement -> error "Expected Utf8Info but got: " ++ show unexpectedElement
+        unexpectedElement -> error "Expected NameAndTypeInfo but got: " ++ show unexpectedElement
+    unexpectedElement -> error "Expected MethodRefInfo but got: " ++ show unexpectedElement
+
+methodParametersFromIndex :: [ConstantInfo] -> Int -> ([String], String)
+methodParametersFromIndex constants index = parseMethodType ([], "V") (methodTypeFromIndex constants index)
+
+memberInfoIsMethod :: [ConstantInfo] -> MemberInfo -> Bool
+memberInfoIsMethod constants info = '(' `elem` memberInfoDescriptor constants info
 
 datatypeDescriptor :: String -> String
 datatypeDescriptor "void" = "V"
 datatypeDescriptor "int" = "I"
 datatypeDescriptor "char" = "C"
-datatypeDescriptor "boolean" = "B"
+datatypeDescriptor "boolean" = "Z"
 datatypeDescriptor x = "L" ++ x ++ ";"
 
-
 memberInfoDescriptor :: [ConstantInfo] -> MemberInfo -> String
-memberInfoDescriptor constants MemberInfo {
+memberInfoDescriptor constants MemberInfo { memberDescriptorIndex = descriptorIndex } = let
-    memberAccessFlags = _,
+            descriptor = constants !! (fromIntegral descriptorIndex - 1)
-    memberNameIndex = _,
-    memberDescriptorIndex = descriptorIndex,
-    memberAttributes = _ } = let
-            descriptor = constants!!((fromIntegral descriptorIndex) - 1)
         in case descriptor of
             Utf8Info descriptorText -> descriptorText
-            _ -> ("Invalid Item at Constant pool index " ++ show descriptorIndex)
+            _ -> "Invalid Item at Constant pool index " ++ show descriptorIndex
-
 
 memberInfoName :: [ConstantInfo] -> MemberInfo -> String
-memberInfoName constants MemberInfo {
+memberInfoName constants MemberInfo { memberNameIndex = nameIndex } = let
-    memberAccessFlags = _,
+            name = constants !! (fromIntegral nameIndex - 1)
-    memberNameIndex = nameIndex,
-    memberDescriptorIndex = _,
-    memberAttributes = _ } = let
-            name = constants!!((fromIntegral nameIndex) - 1)
         in case name of
             Utf8Info nameText -> nameText
-            _ -> ("Invalid Item at Constant pool index " ++ show nameIndex)
+            _ -> "Invalid Item at Constant pool index " ++ show nameIndex
-
 
 returnOperation :: DataType -> Operation
 returnOperation dtype
-    | elem dtype ["int", "char", "boolean"] = Opireturn
+    | dtype `elem` ["int", "char", "boolean"] = Opireturn
     | otherwise                               = Opareturn
 
 binaryOperation :: BinaryOperator -> Operation
@@ -100,53 +119,30 @@ comparisonOperation CompareLessOrEqual    branchLocation = Opif_icmple branchLoc
 comparisonOperation CompareGreaterThan    branchLocation = Opif_icmpgt branchLocation
 comparisonOperation CompareGreaterOrEqual branchLocation = Opif_icmpge branchLocation
 
-findFieldIndex :: [ConstantInfo] -> String -> Maybe Int
+comparisonOffset :: Operation -> Maybe Int
-findFieldIndex constants name = let
+comparisonOffset (Opif_icmpeq offset) = Just $ fromIntegral offset
-        fieldRefNameInfos = [
+comparisonOffset (Opif_icmpne offset) = Just $ fromIntegral offset
-                -- we only skip one entry to get the name since the Java constant pool
+comparisonOffset (Opif_icmplt offset) = Just $ fromIntegral offset
-                -- is 1-indexed (why)
+comparisonOffset (Opif_icmple offset) = Just $ fromIntegral offset
-                (index, constants!!(fromIntegral index + 1))
+comparisonOffset (Opif_icmpgt offset) = Just $ fromIntegral offset
-                | (index, FieldRefInfo classIndex _) <- (zip [1..] constants)
+comparisonOffset (Opif_icmpge offset) = Just $ fromIntegral offset
-            ]
+comparisonOffset anything_else = Nothing
-        fieldRefNames = map (\(index, nameInfo) -> case nameInfo of
-            Utf8Info fieldName -> (index, fieldName)
-            something_else -> error ("Expected UTF8Info but got" ++ show something_else))
-                fieldRefNameInfos
-        fieldIndex = find (\(index, fieldName) -> fieldName == name) fieldRefNames
-    in case fieldIndex of
-        Just (index, _) -> Just index
-        Nothing -> Nothing
-
-findMethodRefIndex :: [ConstantInfo] -> String -> Maybe Int
-findMethodRefIndex constants name = let
-        methodRefNameInfos = [
-                -- we only skip one entry to get the name since the Java constant pool
-                -- is 1-indexed (why)
-                (index, constants!!(fromIntegral index + 1))
-                | (index, MethodRefInfo _ _) <- (zip [1..] constants)
-            ]
-        methodRefNames = map (\(index, nameInfo) -> case nameInfo of
-            Utf8Info methodName -> (index, methodName)
-            something_else -> error ("Expected UTF8Info but got " ++ show something_else))
-                methodRefNameInfos
-        methodIndex = find (\(index, methodName) -> methodName == name) methodRefNames
-    in case methodIndex of
-        Just (index, _) -> Just index
-        Nothing -> Nothing
 
+isComparisonOperation :: Operation -> Bool
+isComparisonOperation op = isJust (comparisonOffset op)
 
 findMethodIndex :: ClassFile -> String -> Maybe Int
 findMethodIndex classFile name = let
         constants = constantPool classFile
     in
-        findIndex (\method -> ((memberInfoIsMethod constants method) && (memberInfoName constants method) == name)) (methods classFile)
+        findIndex (\method -> memberInfoIsMethod constants method && memberInfoName constants method == name) (methods classFile)
 
 findClassIndex :: [ConstantInfo] -> String -> Maybe Int
 findClassIndex constants name = let
-        classNameIndices = [(index, constants!!(fromIntegral nameIndex - 1)) | (index, ClassInfo nameIndex) <- (zip[1..] constants)]
+        classNameIndices = [(index, constants!!(fromIntegral nameIndex - 1)) | (index, ClassInfo nameIndex) <- zip [1..] constants]
         classNames = map (\(index, nameInfo) -> case nameInfo of
             Utf8Info className -> (index, className)
-            something_else -> error("Expected UTF8Info but got " ++ show something_else))
+            something_else -> error ("Expected UTF8Info but got " ++ show something_else))
                 classNameIndices
         desiredClassIndex = find (\(index, className) -> className == name) classNames
     in case desiredClassIndex of
@@ -157,10 +153,10 @@ getKnownMembers :: [ConstantInfo] -> [(Int, (String, String, String))]
 getKnownMembers constants = let
         fieldsClassAndNT = [
                 (index, constants!!(fromIntegral classIndex - 1), constants!!(fromIntegral nameTypeIndex - 1))
-                | (index, FieldRefInfo classIndex nameTypeIndex) <- (zip [1..] constants)
+                | (index, FieldRefInfo classIndex nameTypeIndex) <- zip [1..] constants
             ] ++ [
                 (index, constants!!(fromIntegral classIndex - 1), constants!!(fromIntegral nameTypeIndex - 1))
-                | (index, MethodRefInfo classIndex nameTypeIndex) <- (zip [1..] constants)
+                | (index, MethodRefInfo classIndex nameTypeIndex) <- zip [1..] constants
             ]
 
         fieldsClassNameType = map (\(index, nameInfo, nameTypeInfo) -> case (nameInfo, nameTypeInfo) of
@@ -170,7 +166,7 @@ getKnownMembers constants = let
 
         fieldsResolved = map (\(index, (nameInfo, fnameInfo, ftypeInfo)) -> case (nameInfo, fnameInfo, ftypeInfo) of
             (Utf8Info cname, Utf8Info fname, Utf8Info ftype) -> (index, (cname, fname, ftype))
-            something_else -> error("Expected UTF8Infos but got " ++ show something_else))
+            something_else -> error ("Expected UTF8Infos but got " ++ show something_else))
                 fieldsClassNameType
     in
         fieldsResolved
@@ -179,7 +175,7 @@ getKnownMembers constants = let
 getClassIndex :: [ConstantInfo] -> String -> ([ConstantInfo], Int)
 getClassIndex constants name = case findClassIndex constants name of
     Just index -> (constants, index)
-    Nothing -> (constants ++ [ClassInfo (fromIntegral (length constants)), Utf8Info name], fromIntegral (length constants))
+    Nothing -> (constants ++ [ClassInfo (fromIntegral (length constants) + 2), Utf8Info name], fromIntegral (length constants) + 1)
 
 -- get the index for a field within a class, creating it if it does not exist.
 getFieldIndex :: [ConstantInfo] -> (String, String, String) -> ([ConstantInfo], Int)
@@ -239,7 +235,58 @@ injectFieldInitializers classname vars pre = let
                 otherwise -> Nothing
             ) vars
     in
-        map (\(method) -> case method of
+        map (\method -> case method of
                 MethodDeclaration "void" "<init>" params (TypedStatement "void" (Block statements)) -> MethodDeclaration "void" "<init>" params (TypedStatement "void" (Block (initializers ++ statements)))
-                otherwise -> method
+                _ -> method
             ) pre
+
+-- effect of one instruction/operation on the stack
+operationStackCost :: [ConstantInfo] -> Operation -> Int
+operationStackCost constants Opiadd          = -1
+operationStackCost constants Opisub          = -1
+operationStackCost constants Opimul          = -1
+operationStackCost constants Opidiv          = -1
+operationStackCost constants Opirem          = -1
+operationStackCost constants Opiand          = -1
+operationStackCost constants Opior           = -1
+operationStackCost constants Opixor          = -1
+operationStackCost constants Opineg          =  0
+operationStackCost constants Opdup           =  1
+operationStackCost constants (Opnew _)       =  1
+operationStackCost constants (Opif_icmplt _) = -2
+operationStackCost constants (Opif_icmple _) = -2
+operationStackCost constants (Opif_icmpgt _) = -2
+operationStackCost constants (Opif_icmpge _) = -2
+operationStackCost constants (Opif_icmpeq _) = -2
+operationStackCost constants (Opif_icmpne _) = -2
+operationStackCost constants Opaconst_null   =  1
+operationStackCost constants Opreturn        =  0
+operationStackCost constants Opireturn       = -1
+operationStackCost constants Opareturn       = -1
+operationStackCost constants Opdup_x1        =  1
+operationStackCost constants Oppop           = -1
+operationStackCost constants (Opinvokespecial idx) = let
+        (params, returnType) = methodParametersFromIndex constants (fromIntegral idx)
+    in  (length params + 1) - fromEnum (returnType /= "V")
+operationStackCost constants (Opinvokevirtual idx) = let
+        (params, returnType) = methodParametersFromIndex constants (fromIntegral idx)
+    in  (length params + 1) - fromEnum (returnType /= "V")
+operationStackCost constants (Opgoto _)      =  0
+operationStackCost constants (Opsipush _)    =  1
+operationStackCost constants (Opldc_w _)     =  1
+operationStackCost constants (Opaload _)     =  1
+operationStackCost constants (Opiload _)     =  1
+operationStackCost constants (Opastore _)    = -1
+operationStackCost constants (Opistore _)    = -1
+operationStackCost constants (Opputfield _)  = -2
+operationStackCost constants (Opgetfield _)  = -1
+
+simulateStackOperation :: [ConstantInfo] -> Operation -> (Int, Int) -> (Int, Int)
+simulateStackOperation constants op (cd, md) = let
+        depth = cd + operationStackCost constants op
+    in if depth < 0
+        then error ("Consuming value off of empty stack: " ++ show op)
+        else (depth, max depth md)
+
+maxStackDepth :: [ConstantInfo] -> [Operation] -> Int
+maxStackDepth constants ops = snd $ foldr (simulateStackOperation constants) (0, 0) (reverse ops)

src/Main.hs

@@ -1,6 +1,5 @@
 module Main where
 
-import Example
 import Typecheck
 import Parser.Lexer (alexScanTokens)
 import Parser.JavaParser
@@ -14,18 +13,18 @@ main = do
     args <- getArgs
     let filename = if null args
                    then error "Missing filename, I need to know what to compile"
-                   else args!!0
+                   else head args
     let outputDirectory = takeDirectory filename
     print ("Compiling " ++ filename)
     file <- readFile filename
 
     let untypedAST = parse $ alexScanTokens file
-    let typedAST = (typeCheckCompilationUnit untypedAST)
+    let typedAST = typeCheckCompilationUnit untypedAST
-    let assembledClasses = map (\(typedClass) -> classBuilder typedClass emptyClassFile) typedAST
+    let assembledClasses = map (`classBuilder` emptyClassFile) typedAST
 
-    mapM_ (\(classFile) -> let
+    mapM_ (\classFile -> let
             fileContent = pack (serialize classFile)
-            fileName = outputDirectory ++ "/" ++ (className classFile) ++ ".class"
+            fileName = outputDirectory ++ "/" ++ className classFile ++ ".class"
         in Data.ByteString.writeFile fileName fileContent
             ) assembledClasses
 

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 **********************************
 
@@ -125,18 +129,21 @@ 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
     Nothing -> error $ "Class '" ++ className ++ "' not found."
-    Just (Class _ methods fields) ->
+    Just (Class _ methods _) ->
       -- Find constructor matching the class name with void return type
-      case find (\(MethodDeclaration retType name params _) -> name == "<init>" && retType == "void") methods of
+      case find (\(MethodDeclaration _ name params _) -> name == "<init>") methods of
         -- If no constructor is found, assume standard constructor with no parameters
         Nothing ->
           if null args then
@@ -144,21 +151,28 @@ typeCheckStatementExpression (ConstructorCall className args) symtab classes =
           else
             error $ "No valid constructor found for class '" ++ className ++ "', but arguments were provided."
         Just (MethodDeclaration _ _ params _) ->
-          let
+          let args' = zipWith
-            args' = map (\arg -> typeCheckExpression arg symtab classes) args
+                  (\arg (ParameterDeclaration paramType _) ->
-            -- Extract expected parameter types from the constructor's parameters
+                    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'
-            -- Check if the types of the provided arguments match the expected types
+              typeMatches = zipWith
-            typeMatches = zipWith (\expected actual -> if expected == actual then Nothing else Just (expected, actual)) expectedTypes argTypes
+                  (\expType argType -> (expType == argType || (argType == "null" && isObjectType expType), expType, argType))
-            mismatchErrors = map (\(exp, act) -> "Expected type '" ++ exp ++ "', found '" ++ act ++ "'.") (catMaybes typeMatches)
+                  expectedTypes argTypes
+              mismatches = filter (not . fst3) typeMatches
+              fst3 (a, _, _) = a
           in
-            if length args /= length params then
+            if null mismatches && length args == length params then
-              error $ "Constructor for class '" ++ className ++ "' expects " ++ show (length params) ++ " arguments, but got " ++ show (length args) ++ "."
-            else if not (null mismatchErrors) then
-              error $ unlines $ ("Type mismatch in constructor arguments for class '" ++ className ++ "':") : mismatchErrors
-            else
               TypedStatementExpression className (ConstructorCall className args')
+            else if not (null mismatches) then
+              error $ unlines $ ("Type mismatch in constructor arguments for class '" ++ className ++ "':")
+                  : [ "Expected: " ++ expType ++ ", Found: " ++ argType | (_, expType, argType) <- mismatches ]
+            else
+              error $ "Incorrect number of arguments for constructor of class '" ++ className ++ "'. Expected " ++ show (length expectedTypes) ++ ", found " ++ show (length args) ++ "."
 
 typeCheckStatementExpression (MethodCall expr methodName args) symtab classes =
     let objExprTyped = typeCheckExpression expr symtab classes
@@ -168,20 +182,26 @@ 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, 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."
@@ -251,14 +271,18 @@ 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
@@ -305,13 +329,17 @@ 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')