Merge remote-tracking branch 'origin/master' into create-parser

.gitignore

@@ -8,7 +8,6 @@ cabal-dev
 *.chs.h
 *.dyn_o
 *.dyn_hi
-*.java
 *.class
 *.local~*
 src/Parser/JavaParser.hs

README.md

@@ -5,7 +5,7 @@ Written in Haskell.
 # Cabal Commands
 run main
 ```
-cabal run
+cabal run compiler <FILENAME>
 ```
 
 run tests

Test/JavaSources/Main.java

@@ -0,0 +1,43 @@
+// compile all test files using:
+// ls Test/JavaSources/*.java | grep -v ".*Main.java" | xargs -I {} cabal run compiler {}
+// compile (in project root) using:
+// pushd Test/JavaSources; javac -g:none Main.java; popd
+// afterwards, run using
+// java -ea -cp Test/JavaSources/ Main
+
+public class Main {
+    public static void main(String[] args)
+    {
+        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();
+
+        // constructing a basic class works
+        assert empty != null;
+        // initializers (and default initializers to 0/null) work
+        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.
+        assert recursion.child.child.child.child.child.value == 5;
+        // self-referencing methods work.
+        assert recursion.fibonacci(15) == 610;
+        // intentionally dodgy expressions work
+        assert malicious.assignNegativeIncrement(42) == -42;
+        assert malicious.tripleAddition(1, 2, 3) == 6;
+        for(int i = 0; i < 3; i++)
+        {
+            assert malicious.cursedFormatting(i) == i;
+        }
+    }
+}

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/TestConstructor.java

@@ -0,0 +1,9 @@
+public class TestConstructor
+{
+    public int a = -1;
+
+    public TestConstructor(int initial_value)
+    {
+        a = initial_value;
+    }
+}

Test/JavaSources/TestEmpty.java

@@ -0,0 +1,4 @@
+public class TestEmpty
+{
+    
+}

Test/JavaSources/TestFields.java

@@ -0,0 +1,5 @@
+public class TestFields
+{
+    public int a;
+    public int b = 42;
+}

Test/JavaSources/TestMalicious.java

@@ -0,0 +1,41 @@
+public class TestMalicious {
+    public int assignNegativeIncrement(int n)
+    {
+        return n=-++n+1;
+    }
+
+    public int tripleAddition(int a, int b, int c)
+    {
+        return a+++b+++c++;
+    }
+
+    public int cursedFormatting(int n)
+    {
+        if
+        
+        
+        (n == 0)
+        
+        {
+            
+            return                      ((((0))));
+        }
+
+        else 
+
+        
+        if(n == 
+        
+        1)
+                    {
+            return 
+            
+            
+            1;
+                    }else                 {
+            return 
+            2
+            ;
+                    }
+    }
+}

Test/JavaSources/TestMultipleClasses.java

@@ -0,0 +1,9 @@
+public class TestMultipleClasses
+{
+    public AnotherTestClass a = new AnotherTestClass();
+}
+
+class AnotherTestClass
+{
+    public int a = 42;
+}

Test/JavaSources/TestRecursion.java

@@ -0,0 +1,34 @@
+public class TestRecursion {
+
+    public int value = 0;
+    public TestRecursion child = null;
+
+    public TestRecursion(int n)
+    {
+        this.value = n;
+
+        if(n > 0)
+        {
+            child = new TestRecursion(n - 1);
+        }
+    }
+
+    public int fibonacci(int n)
+    {
+        if(n < 2)
+        {
+            return n;
+        }
+        else
+        {
+            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));
+    }
+}

Test/TestByteCodeGenerator.hs

@@ -1,116 +0,0 @@
-module TestByteCodeGenerator where
-
-import Test.HUnit
-import ByteCode.ClassFile.Generator
-import ByteCode.ClassFile
-import ByteCode.Constants
-import Ast
-
-nakedClass = Class "Testklasse" [] []
-expectedClass = ClassFile {
-        constantPool = [
-            ClassInfo 4,
-            MethodRefInfo 1 3,
-            NameAndTypeInfo 5 6,
-            Utf8Info "java/lang/Object",
-            Utf8Info "<init>",
-            Utf8Info "()V",
-            Utf8Info "Code",
-            ClassInfo 9,
-            Utf8Info "Testklasse"
-        ],
-        accessFlags = accessPublic,
-        thisClass = 8,
-        superClass = 1,
-        fields = [],
-        methods = [],
-        attributes = []
-    }
-
-classWithFields = Class "Testklasse" [] [VariableDeclaration "int" "testvariable" Nothing]
-expectedClassWithFields = ClassFile {
-        constantPool = [
-            ClassInfo 4,
-            MethodRefInfo 1 3,
-            NameAndTypeInfo 5 6,
-            Utf8Info "java/lang/Object",
-            Utf8Info "<init>",
-            Utf8Info "()V",
-            Utf8Info "Code",
-            ClassInfo 9,
-            Utf8Info "Testklasse",
-            FieldRefInfo 8 11,
-            NameAndTypeInfo 12 13,
-            Utf8Info "testvariable",
-            Utf8Info "I"
-        ],
-        accessFlags = accessPublic,
-        thisClass = 8,
-        superClass = 1,
-        fields = [
-            MemberInfo {
-                memberAccessFlags = accessPublic,
-                memberNameIndex = 12,
-                memberDescriptorIndex = 13,
-                memberAttributes = []
-            }
-        ],
-        methods = [],
-        attributes = []
-    }
-
-method = MethodDeclaration "int" "add_two_numbers" [
-    ParameterDeclaration "int" "a",
-    ParameterDeclaration "int" "b" ]
-    (Block [Return (Just (BinaryOperation Addition (Reference "a") (Reference "b")))])
-
-
-classWithMethod = Class "Testklasse" [method] []
-expectedClassWithMethod = ClassFile {
-        constantPool = [
-            ClassInfo 4,
-            MethodRefInfo 1 3,
-            NameAndTypeInfo 5 6,
-            Utf8Info "java/lang/Object",
-            Utf8Info "<init>",
-            Utf8Info "()V",
-            Utf8Info "Code",
-            ClassInfo 9,
-            Utf8Info "Testklasse",
-            FieldRefInfo 8 11,
-            NameAndTypeInfo 12 13,
-            Utf8Info "add_two_numbers",
-            Utf8Info "(II)I"
-        ],
-        accessFlags = accessPublic,
-        thisClass = 8,
-        superClass = 1,
-        fields = [],
-        methods = [
-            MemberInfo {
-                memberAccessFlags = accessPublic,
-                memberNameIndex = 12,
-                memberDescriptorIndex = 13,
-                memberAttributes = [
-                    CodeAttribute {
-                        attributeMaxStack = 420,
-                        attributeMaxLocals = 420,
-                        attributeCode = [Opiadd]
-                    }
-                ]
-            }
-        ],
-        attributes = []
-    }
-
-testBasicConstantPool = TestCase $ assertEqual "basic constant pool" expectedClass $ classBuilder nakedClass emptyClassFile
-testFields = TestCase $ assertEqual "fields in constant pool" expectedClassWithFields $ classBuilder classWithFields emptyClassFile
-testMethodDescriptor = TestCase $ assertEqual "method descriptor" "(II)I" (methodDescriptor method)
-testMethodAssembly = TestCase $ assertEqual "method assembly" expectedClassWithMethod (classBuilder classWithMethod emptyClassFile)
-
-tests = TestList [
-    TestLabel "Basic constant pool" testBasicConstantPool,
-    TestLabel "Fields constant pool" testFields,
-    TestLabel "Method descriptor building" testMethodDescriptor,
-    TestLabel "Method assembly" testMethodAssembly
-    ]

Test/TestSuite.hs

@@ -2,13 +2,11 @@ module Main where
 
 import Test.HUnit
 import TestLexer
-import TestByteCodeGenerator
 import TestParser
 
-
 tests = TestList [
-    TestLabel "TestLexer" TestLexer.tests,
+        TestLabel "TestLexer" TestLexer.tests,
-    TestLabel "TestParser" TestParser.tests,
+        TestLabel "TestParser" TestParser.tests
-    TestLabel "TestByteCodeGenerator" TestByteCodeGenerator.tests]
+    ]
 
 main = do runTestTTAndExit Main.tests

doc/bytecode.md

@@ -0,0 +1,79 @@
+# Bytecodegenerierung
+
+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. Dieser Teil der Aufgabenstellung wurde gemeinsam von Christian Brier und Matthias Raba umgesetzt.
+
+## Codegenerierung
+
+Für die erste der beiden Transformationen (`Getypter AST -> [ClassFile]`) werden die Konzepte der "Builder" und "Assembler" eingeführt. Sie sind wie folgt definiert:
+```
+type ClassFileBuilder a = a -> ClassFile -> ClassFile
+type Assembler a = ([ConstantInfo], [Operation], [String]) -> a -> ([ConstantInfo], [Operation], [String])
+```
+
+Die Idee hinter beiden ist, dass sie jeweils zwei Inputs haben, wobei der Rückgabewert immer den gleichen Typ hat wie einer der inputs. Das erlaubt es, eine Faltung durchzuführen. Ein ClassFileBuilder z.B bekommt als ersten Parameter den AST, und als zweiten Parameter (und Rückgabewert) eine ClassFile. Soll nun eine Klasse gebaut werden, wird der ClassFileBuilder mit dem AST und einer leeren ClassFile aufgerufen. Der Zustand dieser anfangs leeren ClassFile wird durch alle folgenden Builder/Assembler durchgeschleift, was es erlaubt, nach und nach kleinere Transformationen auf sie anzuwenden.
+
+Der Nutzer ruft beispielsweise die Funktion `classBuilder` auf. Diese wendet nach und nach folgende Transformationen an:
+
+```
+        methodsWithInjectedConstructor = injectDefaultConstructor methods
+        methodsWithInjectedInitializers = injectFieldInitializers name fields methodsWithInjectedConstructor
+
+        classFileWithFields = foldr fieldBuilder nakedClassFile fields
+        classFileWithMethods = foldr methodBuilder classFileWithFields methodsWithInjectedInitializers
+        classFileWithAssembledMethods = foldr methodAssembler classFileWithMethods methodsWithInjectedInitializers
+```
+
+Zuerst wird (falls notwendig) ein leerer Defaultkonstruktor in die Classfile eingefügt. Anschließend wird der AST so modifiziert, dass die Initialisierungen für alle Klassenfelder in allen Konstruktoren stattfinden. Nun beginnen die Faltungen:
+
+    1. Hinzufügen aller Klassenfelder
+    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. 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:
+
+`([ConstantInfo], [Operation], [String])`
+
+Dieses repräsentiert:
+
+`(Konstantenpool, Bytecode, Lokale Variablen)`
+
+In der Praxis werden oft nur Bytecode und Konstanten hinzugefügt. Prinzipiell können Assembler auch Code/Konstanten entfernen oder modifizieren. Als Beispiel dient hier der Assembler `assembleExpression`:
+
+```
+assembleExpression (constants, ops, lvars) (TypedExpression _ NullLiteral) =
+    (constants, ops ++ [Opaconst_null], lvars)
+```
+
+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.

doc/generate.sh

@@ -0,0 +1,4 @@
+#!/usr/bin/sh
+
+pandoc bytecode.md -o bytecode.docx
+pandoc bytecode.md -o bytecode.pdf

doc/typecheck.md

@@ -0,0 +1,55 @@
+# Typcheck (Fabian Noll)
+
+## Überblick und Struktur
+
+Die Typprüfung beginnt mit der Funktion `typeCheckCompilationUnit`, die eine Kompilationseinheit als Eingabe erhält. Diese Kompilationseinheit besteht aus einer Liste von Klassen. Jede Klasse wird einzeln durch die Funktion `typeCheckClass` überprüft. Innerhalb dieser Funktion wird eine Symboltabelle erstellt, die den Namen der Klasse als Typ und `this` als Identifier enthält. Diese Symboltabelle wird verwendet, um Typinformationen nach dem Lokalitätsprinzip während der Typprüfung zugänglich zu machen und zu verwalten.
+
+Die Typprüfung einer Klasse umfasst die Überprüfung aller Methoden und Felder. Die Methode `typeCheckMethodDeclaration` ist für die Typprüfung einzelner Methodendeklarationen verantwortlich. Sie überprüft den Rückgabetyp der Methode, die Parameter und den Methodenrumpf. Der Methodenrumpf wird durch rekursive Aufrufe von `typeCheckStatement` überprüft, die verschiedene Arten von Anweisungen wie If-Anweisungen, While-Schleifen, Rückgabeanweisungen und Blockanweisungen behandelt.
+
+## Ablauf und Symboltabellen
+
+Eine zentrale Komponente des Typecheckers ist die Symboltabelle (symtab), die Informationen über die Bezeichner und ihre zugehörigen Datentypen speichert. Die Symboltabelle wird kontinuierlich angepasst, während der Typechecker die verschiedenen Teile des Programms durchläuft.
+
+### Anpassung der Symboltabelle
+
+- **Klassenkontext**:
+  Beim Typcheck einer Klasse wird eine initiale Symboltabelle erstellt, die die `this`-Referenz enthält. Dies geschieht in der Funktion `typeCheckClass`.
+
+- **Methodenkontext**:
+  Innerhalb einer Methode wird die Symboltabelle um die Parameter der Methode erweitert sowie den Rückgabetyp der Methode, um die einzelnen Returns dagegen zu prüfen. Dies geschieht in `typeCheckMethodDeclaration`.
+
+- **Blockkontext**:
+  Bei der Überprüfung eines Blocks (`typeCheckStatement` für Block) wird die Symboltabelle für jede Anweisung innerhalb des Blocks aktualisiert. Lokale Variablen, die innerhalb des Blocks deklariert werden, werden zur Symboltabelle hinzugefügt. Das bedeutet, dass automatisch, sobald der Block zu Ende ist, alle dort deklarierten Variablen danach nicht mehr zugänglich sind.
+
+### Unterscheidung zwischen lokalen und Feldvariablen
+
+Bei der Typprüfung von Referenzen (`typeCheckExpression` für Reference) wird zuerst in der Symboltabelle nach dem Bezeichner gesucht. Sollte dieser gefunden werden, handelt es sich um eine lokale Variable. Wenn der Bezeichner nicht gefunden wird, wird angenommen, dass es sich um eine Feldvariable handelt. In diesem Fall wird die Klasse, zu der die `this`-Referenz gehört, durchsucht, um die Feldvariable zu finden. Dies ermöglicht die Unterscheidung zwischen lokalen Variablen und Feldvariablen. Dies ist auch nur möglich, da wir die Feldvariablen und Methoden nicht in die Symboltabelle gelegt haben und stattdessen nur die `this`-Referenz.
+
+## Fehlerbehandlung
+
+Ein zentraler Aspekt des Typecheckers ist die Fehlerbehandlung. Bei Typinkonsistenzen oder ungültigen Operationen werden aussagekräftige Fehlermeldungen generiert. Beispiele für solche Fehlermeldungen sind:
+
+- **Typinkonsistenzen**:
+  Wenn der Rückgabetyp einer Methode nicht mit dem deklarierten Rückgabetyp übereinstimmt. Oder aber auch die Anzahl der Parameter nicht übereinstimmt.
+
+- **Ungültige Operationen**:
+  Wenn eine arithmetische Operation auf inkompatiblen Typen durchgeführt wird.
+
+- **Nicht gefundene Bezeichner**:
+  Wenn eine Referenz auf eine nicht definierte Variable verweist.
+
+Diese Fehlermeldungen helfen Entwicklern, die Ursachen von Typfehlern schnell zu identifizieren und zu beheben. Generell sind diese oftmals sehr spezifisch, was das Problem recht schnell identifizieren sollte. Z.B. falsche Reihenfolge / falsche Typen der Parameter beim Methodenaufruf sind direkt erkennbar.
+
+## Typprüfung von Kontrollstrukturen und Blöcken
+
+### If-Anweisungen
+
+Bei der Typprüfung einer If-Anweisung (`typeCheckStatement` für If) wird zuerst der Typ der Bedingung überprüft, um sicherzustellen, dass es sich um einen booleschen Ausdruck handelt. Anschließend werden die Then- und Else-Zweige geprüft. Der Typ der If-Anweisung selbst wird durch die Vereinheitlichung der Typen der Then- und Else-Zweige bestimmt. Falls einer der Zweige keinen Rückgabewert hat, wird angenommen, dass der Rückgabewert `void` ist. Dies wurde so gelöst, um im Typchecker feststellen zu können, ob beide Zweige einen Return haben. Wenn nur einer der Zweige ein Return hat, wird im umliegenden Block ein weiteres benötigt, was durch den Typ `void` erzwungen wird. Dadurch weiß der Typchecker Bescheid.
+
+### Block-Anweisungen
+
+Die Typprüfung eines Blocks erfolgt in `typeCheckStatement` für Block. Jede Anweisung im Block wird nacheinander überprüft und die Symboltabelle wird entsprechend aktualisiert. Der Typ des Blocks wird durch die Vereinheitlichung der Typen aller Anweisungen im Block bestimmt. Wenn der Block keine Anweisungen hat, wird der Typ `void` angenommen.
+
+### Rückgabeanweisungen
+
+Die Typprüfung einer Rückgabeanweisung (`typeCheckStatement` für Return) überprüft, ob der Rückgabewert der Anweisung mit dem deklarierten Rückgabetyp der Methode übereinstimmt. Dafür wurde zu Beginn der Methodentypprüfung der Rückgabetyp der Methode in die Symboltabelle eingetragen. Wenn der Rückgabewert `null` ist, wird überprüft, ob der deklarierte Rückgabetyp ein Objekttyp ist. Dies stellt sicher, dass Methoden immer den korrekten Typ zurückgeben. Generell wird bei der Prüfung nach dem UpperBound geschaut und ebenfalls wird nachgeschaut, ob, wenn der Rückgabetyp `Object` ist, der Return-Wert auch eine tatsächlich existierende Klasse ist, indem in die Klassentabelle geschaut wird.

project.cabal

@@ -10,20 +10,21 @@ executable compiler
                         array,
                         HUnit,
                         utf8-string,
-                        bytestring
+                        bytestring,
+                        filepath
     default-language:   Haskell2010
-    hs-source-dirs:     src,
+    hs-source-dirs:     src
-                        src/ByteCode,
-                        src/ByteCode/ClassFile
     build-tool-depends: alex:alex, happy:happy
     other-modules:      Parser.Lexer,
-                        Parser.JavaParser
+                        Parser.JavaParser,
                         Ast,
                         Example,
                         Typecheck,
+                        ByteCode.Util,
                         ByteCode.ByteUtil,
                         ByteCode.ClassFile,
-                        ByteCode.ClassFile.Generator,
+                        ByteCode.Assembler,
+                        ByteCode.Builder,
                         ByteCode.Constants
 
 test-suite tests
@@ -34,15 +35,17 @@ test-suite tests
                         array,
                         HUnit,
                         utf8-string,
-                        bytestring
+                        bytestring,
+                        filepath
     build-tool-depends: alex:alex, happy:happy
     other-modules:      Parser.Lexer,
                         Parser.JavaParser,
                         Ast,
                         TestLexer,
                         TestParser,
-                        TestByteCodeGenerator,
+                        ByteCode.Util,
                         ByteCode.ByteUtil,
                         ByteCode.ClassFile,
-                        ByteCode.ClassFile.Generator,
+                        ByteCode.Assembler,
+                        ByteCode.Builder,
                         ByteCode.Constants

src/ByteCode/Assembler.hs

@@ -0,0 +1,275 @@
+module ByteCode.Assembler where
+
+import ByteCode.Constants
+import ByteCode.ClassFile (ClassFile (..), ConstantInfo (..), MemberInfo(..), Operation(..), Attribute(..), opcodeEncodingLength)
+import ByteCode.Util
+import Ast
+import Data.Char
+import Data.List
+import Data.Word
+
+type Assembler a = ([ConstantInfo], [Operation], [String]) -> a -> ([ConstantInfo], [Operation], [String])
+
+assembleExpression :: Assembler Expression
+assembleExpression (constants, ops, lvars) (TypedExpression _ (BinaryOperation op a b))
+    | 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)
+    | 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
+            cmp_ops = [cmp_op, Opsipush 0, Opgoto 6, Opsipush 1]
+        in
+            (bConstants, bOps ++ cmp_ops, lvars)
+
+assembleExpression (constants, ops, lvars) (TypedExpression _ (BinaryOperation NameResolution (TypedExpression atype a) (TypedExpression btype (FieldVariable b)))) = let
+        (fConstants, fieldIndex) = getFieldIndex constants (atype, b, datatypeDescriptor btype)
+        (aConstants, aOps, _) = assembleExpression (fConstants, ops, lvars) (TypedExpression atype a)
+    in
+        (aConstants, aOps ++ [Opgetfield (fromIntegral fieldIndex)], lvars)
+
+assembleExpression (constants, ops, lvars) (TypedExpression _ (CharacterLiteral literal)) =
+    (constants, ops ++ [Opsipush (fromIntegral (ord literal))], lvars)
+
+assembleExpression (constants, ops, lvars) (TypedExpression _ (BooleanLiteral literal)) =
+    (constants, ops ++ [Opsipush (if literal then 1 else 0)], lvars)
+
+assembleExpression (constants, ops, lvars) (TypedExpression _ (IntegerLiteral literal))
+    | literal <= 32767 && literal >= -32768 = (constants, ops ++ [Opsipush (fromIntegral literal)], lvars)
+    | otherwise = (constants ++ [IntegerInfo (fromIntegral literal)], ops ++ [Opldc_w (fromIntegral (1 + length constants))], lvars)
+
+assembleExpression (constants, ops, lvars) (TypedExpression _ NullLiteral) =
+    (constants, ops ++ [Opaconst_null], lvars)
+
+assembleExpression (constants, ops, lvars) (TypedExpression etype (UnaryOperation Not expr)) = let
+        (exprConstants, exprOps, _) = assembleExpression (constants, ops, lvars) expr
+        newConstant = fromIntegral (1 + length exprConstants)
+    in case etype of
+        "int" -> (exprConstants ++ [IntegerInfo 0x7FFFFFFF], exprOps ++ [Opldc_w newConstant, Opixor], lvars)
+        "char" -> (exprConstants, exprOps ++ [Opsipush 0xFFFF, Opixor], lvars)
+        "boolean" -> (exprConstants, exprOps ++ [Opsipush 0x01, Opixor], lvars)
+
+assembleExpression (constants, ops, lvars) (TypedExpression _ (UnaryOperation Minus expr)) = let
+        (exprConstants, exprOps, _) = assembleExpression (constants, ops, lvars) expr
+    in
+        (exprConstants, exprOps ++ [Opineg], lvars)
+
+assembleExpression (constants, ops, lvars) (TypedExpression dtype (LocalVariable name))
+    | name == "this" = (constants, ops ++ [Opaload 0], lvars)
+    | otherwise = let
+            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)
+            Nothing -> error ("No such local variable found in local variable pool: " ++ name)
+
+assembleExpression (constants, ops, lvars) (TypedExpression dtype (StatementExpressionExpression stmtexp)) =
+        assembleStatementExpression (constants, ops, lvars) stmtexp
+
+assembleExpression _ expr = error ("Unknown expression: " ++ show expr)
+
+assembleNameChain :: Assembler Expression
+assembleNameChain input (TypedExpression _ (BinaryOperation NameResolution (TypedExpression atype a) (TypedExpression _ (FieldVariable _)))) =
+        assembleExpression input (TypedExpression atype a)
+assembleNameChain input expr = assembleExpression input expr
+
+
+assembleStatementExpression :: Assembler StatementExpression
+assembleStatementExpression
+    (constants, ops, lvars)
+    (TypedStatementExpression _ (Assignment (TypedExpression dtype receiver) expr)) = let
+        target = resolveNameChain (TypedExpression dtype receiver)
+    in case target of
+        (TypedExpression dtype (LocalVariable name)) -> let
+                localIndex = elemIndex name lvars
+                (constants_a, ops_a, _) = assembleExpression (constants, ops, lvars) expr
+                isPrimitive = elem dtype ["char", "boolean", "int"]
+            in case localIndex of
+                Just index -> (constants_a, ops_a ++ if isPrimitive then [Opdup, Opistore (fromIntegral index)] else [Opastore (fromIntegral index)], lvars)
+                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
+                (TypedExpression otype _) -> let
+                        (constants_f, fieldIndex) = getFieldIndex constants (otype, name, datatypeDescriptor dtype)
+                        (constants_r, ops_r, _) = assembleNameChain (constants_f, ops, lvars) (TypedExpression dtype receiver)
+                        (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)
+
+assembleStatementExpression
+    (constants, ops, lvars)
+    (TypedStatementExpression _ (PreIncrement (TypedExpression dtype receiver))) = let
+        target = resolveNameChain (TypedExpression dtype receiver)
+    in case target of
+        (TypedExpression dtype (LocalVariable name)) -> let
+                localIndex = elemIndex name lvars
+                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)
+        (TypedExpression dtype (FieldVariable name)) -> let
+                owner = resolveNameChainOwner (TypedExpression dtype receiver)
+            in case owner of
+                (TypedExpression otype _) -> let
+                        (constants_f, fieldIndex) = getFieldIndex constants (otype, name, datatypeDescriptor dtype)
+                        (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)
+
+assembleStatementExpression
+    (constants, ops, lvars)
+    (TypedStatementExpression _ (PreDecrement (TypedExpression dtype receiver))) = let
+        target = resolveNameChain (TypedExpression dtype receiver)
+    in case target of
+        (TypedExpression dtype (LocalVariable name)) -> let
+                localIndex = elemIndex name lvars
+                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)
+        (TypedExpression dtype (FieldVariable name)) -> let
+                owner = resolveNameChainOwner (TypedExpression dtype receiver)
+            in case owner of
+                (TypedExpression otype _) -> let
+                        (constants_f, fieldIndex) = getFieldIndex constants (otype, name, datatypeDescriptor dtype)
+                        (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)
+
+assembleStatementExpression
+    (constants, ops, lvars)
+    (TypedStatementExpression _ (PostIncrement (TypedExpression dtype receiver))) = let
+        target = resolveNameChain (TypedExpression dtype receiver)
+    in case target of
+        (TypedExpression dtype (LocalVariable name)) -> let
+                localIndex = elemIndex name lvars
+                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)
+        (TypedExpression dtype (FieldVariable name)) -> let
+                owner = resolveNameChainOwner (TypedExpression dtype receiver)
+            in case owner of
+                (TypedExpression otype _) -> let
+                        (constants_f, fieldIndex) = getFieldIndex constants (otype, name, datatypeDescriptor dtype)
+                        (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)
+
+assembleStatementExpression
+    (constants, ops, lvars)
+    (TypedStatementExpression _ (PostDecrement (TypedExpression dtype receiver))) = let
+        target = resolveNameChain (TypedExpression dtype receiver)
+    in case target of
+        (TypedExpression dtype (LocalVariable name)) -> let
+                localIndex = elemIndex name lvars
+                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)
+        (TypedExpression dtype (FieldVariable name)) -> let
+                owner = resolveNameChainOwner (TypedExpression dtype receiver)
+            in case owner of
+                (TypedExpression otype _) -> let
+                        (constants_f, fieldIndex) = getFieldIndex constants (otype, name, datatypeDescriptor dtype)
+                        (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)
+
+assembleStatementExpression
+    (constants, ops, lvars)
+    (TypedStatementExpression rtype (MethodCall (TypedExpression otype receiver) name params)) = let
+        (constants_r, ops_r, lvars_r) = assembleExpression (constants, ops, lvars) (TypedExpression otype receiver)
+        (constants_p, ops_p, lvars_p) = foldl assembleExpression (constants_r, ops_r, lvars_r) params
+        (constants_m, methodIndex) = getMethodIndex constants_p (otype, name, methodDescriptorFromParamlist params rtype)
+    in
+        (constants_m, ops_p ++ [Opinvokevirtual (fromIntegral methodIndex)], lvars_p)
+
+assembleStatementExpression
+    (constants, ops, lvars)
+    (TypedStatementExpression rtype (ConstructorCall name params)) = let
+        (constants_c, classIndex) = getClassIndex constants name
+        (constants_p, ops_p, lvars_p) = foldl assembleExpression (constants_c, ops ++ [Opnew (fromIntegral classIndex), Opdup], lvars) params
+        (constants_m, methodIndex) = getMethodIndex constants_p (name, "<init>", methodDescriptorFromParamlist params "void")
+    in
+        (constants_m, ops_p ++ [Opinvokespecial (fromIntegral methodIndex)], lvars_p)
+
+
+assembleStatement :: Assembler Statement
+assembleStatement (constants, ops, lvars) (TypedStatement stype (Return expr)) = case expr of
+    Nothing -> (constants, ops ++ [Opreturn], lvars)
+    Just expr -> let
+            (expr_constants, expr_ops, _) = assembleExpression (constants, ops, lvars) expr
+        in
+            (expr_constants, expr_ops ++ [returnOperation stype], lvars)
+
+assembleStatement (constants, ops, lvars) (TypedStatement _ (Block statements)) =
+    foldl assembleStatement (constants, ops, lvars) statements
+
+assembleStatement (constants, ops, lvars) (TypedStatement dtype (If expr if_stmt else_stmt)) = let
+        (constants_cmp, ops_cmp, _) = assembleExpression (constants, [], lvars) expr
+        (constants_ifa, ops_ifa, _) = assembleStatement (constants_cmp, [], lvars) if_stmt
+        (constants_elsea, ops_elsea, _) = case else_stmt of
+            Nothing -> (constants_ifa, [], lvars)
+            Just stmt -> assembleStatement (constants_ifa, [], lvars) stmt
+        -- +6 because we insert 2 gotos, one for if, one for else
+        if_length = sum (map opcodeEncodingLength ops_ifa)
+        -- +3 because we need to account for the goto in the if statement.
+        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)
+        _ -> (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
+        (constants_stmta, ops_stmta, _) = assembleStatement (constants_cmp, [], lvars) stmt
+        -- +3 because we insert 2 gotos, one for the comparison, one for the goto back to the comparison
+        stmt_length = sum (map opcodeEncodingLength ops_stmta) + 6
+        entire_length = stmt_length + sum (map opcodeEncodingLength ops_cmp)
+    in
+        (constants_stmta, ops ++ ops_cmp ++ [Opsipush 0, Opif_icmpeq stmt_length] ++ ops_stmta ++ [Opgoto (-entire_length)], lvars)
+
+assembleStatement (constants, ops, lvars) (TypedStatement _ (LocalVariableDeclaration (VariableDeclaration dtype name expr))) = let
+        isPrimitive = elem dtype ["char", "boolean", "int"]
+        (constants_init, ops_init, _) = case expr of
+            Just exp -> assembleExpression (constants, ops, lvars) exp
+            Nothing -> (constants, ops ++ if isPrimitive then [Opsipush 0] else [Opaconst_null], lvars)
+        localIndex = fromIntegral (length lvars)
+        storeLocal = if isPrimitive then [Opistore localIndex] else [Opastore localIndex]
+    in
+        (constants_init, ops_init ++ storeLocal, lvars ++ [name])
+
+assembleStatement (constants, ops, lvars) (TypedStatement _ (StatementExpressionStatement expr)) = let
+        (constants_e, ops_e, lvars_e) = assembleStatementExpression (constants, ops, lvars) expr
+    in
+        (constants_e, ops_e ++ [Oppop], lvars_e)
+
+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
+        in
+            (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)
+        _ -> foldl assembleStatement (constants, ops, lvars) statements
+assembleMethod _ (MethodDeclaration _ _ _ stmt) = error ("Typed block expected for method body, got: " ++ show stmt)

src/ByteCode/Builder.hs

@@ -0,0 +1,122 @@
+module ByteCode.Builder where
+
+import ByteCode.Constants
+import ByteCode.ClassFile (ClassFile (..), ConstantInfo (..), MemberInfo(..), Operation(..), Attribute(..), opcodeEncodingLength)
+import ByteCode.Assembler
+import ByteCode.Util
+import Ast
+import Data.Char
+import Data.List
+import Data.Word
+
+type ClassFileBuilder a = a -> ClassFile -> ClassFile
+
+fieldBuilder :: ClassFileBuilder VariableDeclaration
+fieldBuilder (VariableDeclaration datatype name _) input = let
+        baseIndex = 1 + length (constantPool input)
+        constants = [
+                FieldRefInfo (fromIntegral (thisClass input)) (fromIntegral (baseIndex + 1)),
+                NameAndTypeInfo (fromIntegral (baseIndex + 2)) (fromIntegral (baseIndex + 3)),
+                Utf8Info name,
+                Utf8Info (datatypeDescriptor datatype)
+            ]
+        field = MemberInfo {
+            memberAccessFlags = accessPublic,
+            memberNameIndex = fromIntegral (baseIndex + 2),
+            memberDescriptorIndex = fromIntegral (baseIndex + 3),
+            memberAttributes = []
+            }
+    in
+        input {
+            constantPool = constantPool input ++ constants,
+            fields = fields input ++ [field]
+        }
+
+
+
+methodBuilder :: ClassFileBuilder MethodDeclaration
+methodBuilder (MethodDeclaration returntype name parameters statement) input = let
+        baseIndex = 1 + length (constantPool input)
+        constants = [
+                MethodRefInfo (fromIntegral (thisClass input)) (fromIntegral (baseIndex + 1)),
+                NameAndTypeInfo (fromIntegral (baseIndex + 2)) (fromIntegral (baseIndex + 3)),
+                Utf8Info name,
+                Utf8Info (methodDescriptor (MethodDeclaration returntype name parameters (Block [])))
+            ]
+
+        method = MemberInfo {
+            memberAccessFlags = accessPublic,
+            memberNameIndex = fromIntegral (baseIndex + 2),
+            memberDescriptorIndex = fromIntegral (baseIndex + 3),
+            memberAttributes = []
+            }
+    in
+        input {
+            constantPool = constantPool input ++ constants,
+            methods = methods input ++ [method]
+        }
+
+
+methodAssembler :: ClassFileBuilder MethodDeclaration
+methodAssembler (MethodDeclaration returntype name parameters statement) input = let
+        methodConstantIndex = findMethodIndex input name
+    in case methodConstantIndex of
+        Nothing -> error ("Cannot find method entry in method pool for method: " ++ name)
+        Just index -> let
+                declaration = MethodDeclaration returntype name parameters statement
+                paramNames = "this" : [name | ParameterDeclaration _ name <- parameters]
+            in case splitAt index (methods input) of
+                (pre, []) -> input
+                (pre, method : post) -> let
+                        (constants, bytecode, aParamNames) = assembleMethod (constantPool input, [], paramNames) declaration
+                        assembledMethod = method {
+                            memberAttributes = [
+                                CodeAttribute {
+                                    attributeMaxStack = fromIntegral $ maxStackDepth constants bytecode,
+                                    attributeMaxLocals = fromIntegral $ length aParamNames,
+                                    attributeCode = bytecode
+                                }
+                            ]
+                        }
+                    in
+                        input {
+                            constantPool = constants,
+                            methods = pre ++ (assembledMethod : post)
+                        }
+
+
+classBuilder :: ClassFileBuilder Class
+classBuilder (Class name methods fields) _ = let
+        baseConstants = [
+            ClassInfo 4,
+            MethodRefInfo 1 3,
+            NameAndTypeInfo 5 6,
+            Utf8Info "java/lang/Object",
+            Utf8Info "<init>",
+            Utf8Info "()V",
+            Utf8Info "Code",
+            ClassInfo 9,
+            Utf8Info name
+            ]
+        nakedClassFile = ClassFile {
+            constantPool = baseConstants,
+            accessFlags = accessPublic,
+            thisClass = 8,
+            superClass = 1,
+            fields = [],
+            methods = [],
+            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
+    in
+        classFileWithAssembledMethods

src/ByteCode/ByteUtil.hs

@@ -1,7 +1,6 @@
-module ByteCode.ByteUtil(unpackWord16, unpackWord32) where
+module ByteCode.ByteUtil where
 
 import Data.Word ( Word8, Word16, Word32 )
-import Data.Int
 import Data.Bits
 
 unpackWord16 :: Word16 -> [Word8]

src/ByteCode/ClassFile.hs

@@ -1,19 +1,11 @@
-module ByteCode.ClassFile(
+module ByteCode.ClassFile where
-    ConstantInfo(..),
-    Attribute(..),
-    MemberInfo(..),
-    ClassFile(..),
-    Operation(..),
-    serialize,
-    emptyClassFile
-) where
 
 import Data.Word
 import Data.Int
 import Data.ByteString (unpack)
 import Data.ByteString.UTF8 (fromString)
-import ByteCode.ByteUtil
 import ByteCode.Constants
+import ByteCode.ByteUtil
 
 data ConstantInfo = ClassInfo Word16
                   | FieldRefInfo Word16 Word16
@@ -27,10 +19,13 @@ data Operation = Opiadd
                | Opisub
                | Opimul
                | Opidiv
+               | Opirem
                | Opiand
                | Opior
                | Opixor
                | Opineg
+               | Opdup
+               | Opnew Word16
                | Opif_icmplt Word16
                | Opif_icmple Word16
                | Opif_icmpgt Word16
@@ -41,6 +36,11 @@ data Operation = Opiadd
                | Opreturn
                | Opireturn
                | Opareturn
+               | Opdup_x1
+               | Oppop
+               | Opinvokespecial Word16
+               | Opinvokevirtual Word16
+               | Opgoto Word16
                | Opsipush Word16
                | Opldc_w Word16
                | Opaload Word16
@@ -48,7 +48,7 @@ data Operation = Opiadd
                | Opastore Word16
                | Opistore Word16
                | Opputfield Word16
-               | OpgetField Word16
+               | Opgetfield Word16
     deriving (Show, Eq)
 
 
@@ -87,6 +87,50 @@ emptyClassFile = ClassFile {
         attributes = []
     }
 
+className :: ClassFile -> String
+className classFile = let
+        classInfo = constantPool classFile !! fromIntegral (thisClass classFile)
+    in case classInfo of
+        Utf8Info className -> className
+        unexpected_element -> error ("expected Utf8Info but got: " ++ show unexpected_element)
+
+
+opcodeEncodingLength :: Operation -> Word16
+opcodeEncodingLength Opiadd                 = 1
+opcodeEncodingLength Opisub                 = 1
+opcodeEncodingLength Opimul                 = 1
+opcodeEncodingLength Opidiv                 = 1
+opcodeEncodingLength Opirem                 = 1
+opcodeEncodingLength Opiand                 = 1
+opcodeEncodingLength Opior                  = 1
+opcodeEncodingLength Opixor                 = 1
+opcodeEncodingLength Opineg                 = 1
+opcodeEncodingLength Opdup                  = 1
+opcodeEncodingLength (Opnew _)              = 3
+opcodeEncodingLength (Opif_icmplt _)        = 3
+opcodeEncodingLength (Opif_icmple _)        = 3
+opcodeEncodingLength (Opif_icmpgt _)        = 3
+opcodeEncodingLength (Opif_icmpge _)        = 3
+opcodeEncodingLength (Opif_icmpeq _)        = 3
+opcodeEncodingLength (Opif_icmpne _)        = 3
+opcodeEncodingLength Opaconst_null          = 1
+opcodeEncodingLength Opreturn               = 1
+opcodeEncodingLength Opireturn              = 1
+opcodeEncodingLength Opareturn              = 1
+opcodeEncodingLength Opdup_x1               = 1
+opcodeEncodingLength Oppop                  = 1
+opcodeEncodingLength (Opinvokespecial _)    = 3
+opcodeEncodingLength (Opinvokevirtual _)    = 3
+opcodeEncodingLength (Opgoto _)             = 3
+opcodeEncodingLength (Opsipush _)           = 3
+opcodeEncodingLength (Opldc_w _)            = 3
+opcodeEncodingLength (Opaload _)            = 4
+opcodeEncodingLength (Opiload _)            = 4
+opcodeEncodingLength (Opastore _)           = 4
+opcodeEncodingLength (Opistore _)           = 4
+opcodeEncodingLength (Opputfield _)         = 3
+opcodeEncodingLength (Opgetfield _)         = 3
+
 class Serializable a where
     serialize :: a -> [Word8]
 
@@ -108,41 +152,49 @@ instance Serializable MemberInfo where
                     ++ concatMap serialize (memberAttributes member)
 
 instance Serializable Operation where
-    serialize Opiadd               = [0x60]
+    serialize Opiadd                    = [0x60]
-    serialize Opisub               = [0x64]
+    serialize Opisub                    = [0x64]
-    serialize Opimul               = [0x68]
+    serialize Opimul                    = [0x68]
-    serialize Opidiv               = [0x6C]
+    serialize Opidiv                    = [0x6C]
-    serialize Opiand               = [0x7E]
+    serialize Opirem                    = [0x70]
-    serialize Opior                = [0x80]
+    serialize Opiand                    = [0x7E]
-    serialize Opixor               = [0x82]
+    serialize Opior                     = [0x80]
-    serialize Opineg               = [0x74]
+    serialize Opixor                    = [0x82]
-    serialize (Opif_icmplt branch) = 0xA1 : unpackWord16 branch
+    serialize Opineg                    = [0x74]
-    serialize (Opif_icmple branch) = 0xA4 : unpackWord16 branch
+    serialize Opdup                     = [0x59]
-    serialize (Opif_icmpgt branch) = 0xA3 : unpackWord16 branch
+    serialize (Opnew index)             = 0xBB : unpackWord16 index
-    serialize (Opif_icmpge branch) = 0xA2 : unpackWord16 branch
+    serialize (Opif_icmplt branch)      = 0xA1 : unpackWord16 branch
-    serialize (Opif_icmpeq branch) = 0x9F : unpackWord16 branch
+    serialize (Opif_icmple branch)      = 0xA4 : unpackWord16 branch
-    serialize (Opif_icmpne branch) = 0xA0 : unpackWord16 branch
+    serialize (Opif_icmpgt branch)      = 0xA3 : unpackWord16 branch
-    serialize Opaconst_null        = [0x01]
+    serialize (Opif_icmpge branch)      = 0xA2 : unpackWord16 branch
-    serialize Opreturn             = [0xB1]
+    serialize (Opif_icmpeq branch)      = 0x9F : unpackWord16 branch
-    serialize Opireturn            = [0xAC]
+    serialize (Opif_icmpne branch)      = 0xA0 : unpackWord16 branch
-    serialize Opareturn            = [0xB0]
+    serialize Opaconst_null             = [0x01]
-    serialize (Opsipush index)     = 0x11 : unpackWord16 index
+    serialize Opreturn                  = [0xB1]
-    serialize (Opldc_w index)      = 0x13 : unpackWord16 index
+    serialize Opireturn                 = [0xAC]
-    serialize (Opaload index)      = [0xC4, 0x19] ++ unpackWord16 index
+    serialize Opareturn                 = [0xB0]
-    serialize (Opiload index)      = [0xC4, 0x15] ++ unpackWord16 index
+    serialize Opdup_x1                  = [0x5A]
-    serialize (Opastore index)     = [0xC4, 0x3A] ++ unpackWord16 index
+    serialize Oppop                     = [0x57]
-    serialize (Opistore index)     = [0xC4, 0x36] ++ unpackWord16 index
+    serialize (Opinvokespecial index)   = 0xB7 : unpackWord16 index
-    serialize (Opputfield index)   = 0xB5 : unpackWord16 index
+    serialize (Opinvokevirtual index)   = 0xB6 : unpackWord16 index
-    serialize (OpgetField index)   = 0xB4 : unpackWord16 index
+    serialize (Opgoto index)            = 0xA7 : unpackWord16 index
+    serialize (Opsipush index)          = 0x11 : unpackWord16 index
+    serialize (Opldc_w index)           = 0x13 : unpackWord16 index
+    serialize (Opaload index)           = [0xC4, 0x19] ++ unpackWord16 index
+    serialize (Opiload index)           = [0xC4, 0x15] ++ unpackWord16 index
+    serialize (Opastore index)          = [0xC4, 0x3A] ++ unpackWord16 index
+    serialize (Opistore index)          = [0xC4, 0x36] ++ unpackWord16 index
+    serialize (Opputfield index)        = 0xB5 : unpackWord16 index
+    serialize (Opgetfield index)        = 0xB4 : unpackWord16 index
 
 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
@@ -151,7 +203,7 @@ instance Serializable Attribute where
             ++ unpackWord16 0                                               -- attributes_count
 
 instance Serializable ClassFile where
-    serialize classfile  = unpackWord32 0xC0FEBABE                                           -- magic
+    serialize classfile  = unpackWord32 0xCAFEBABE                                           -- magic
                         ++ unpackWord16 0                                                    -- minor version
                         ++ unpackWord16 49                                                   -- major version
                         ++ unpackWord16 (fromIntegral (1 + length (constantPool classfile))) -- constant pool count

src/ByteCode/ClassFile/Generator.hs

@@ -1,169 +0,0 @@
-module ByteCode.ClassFile.Generator(
-    classBuilder,
-    datatypeDescriptor,
-    methodParameterDescriptor,
-    methodDescriptor,
-) where
-
-import ByteCode.Constants
-import ByteCode.ClassFile (ClassFile (..), ConstantInfo (..), MemberInfo(..), Operation(..), Attribute(..))
-import Ast
-import Data.Char
-
-
-type ClassFileBuilder a = a -> ClassFile -> ClassFile
-
-
-datatypeDescriptor :: String -> String
-datatypeDescriptor "void" = "V"
-datatypeDescriptor "int" = "I"
-datatypeDescriptor "char" = "C"
-datatypeDescriptor "boolean" = "B"
-datatypeDescriptor x = "L" ++ x
-
-methodParameterDescriptor :: String -> String
-methodParameterDescriptor "void" = "V"
-methodParameterDescriptor "int" = "I"
-methodParameterDescriptor "char" = "C"
-methodParameterDescriptor "boolean" = "B"
-methodParameterDescriptor x = "L" ++ x ++ ";"
-
-methodDescriptor :: MethodDeclaration -> String
-methodDescriptor (MethodDeclaration returntype _ parameters _) = let 
-        parameter_types = [datatype | ParameterDeclaration datatype _ <- parameters]
-    in
-        "("
-        ++ (concat (map methodParameterDescriptor parameter_types))
-        ++ ")"
-        ++ datatypeDescriptor returntype
-
-classBuilder :: ClassFileBuilder Class
-classBuilder (Class name methods fields) _ = let
-        baseConstants = [
-            ClassInfo 4,
-            MethodRefInfo 1 3,
-            NameAndTypeInfo 5 6,
-            Utf8Info "java/lang/Object",
-            Utf8Info "<init>",
-            Utf8Info "()V",
-            Utf8Info "Code"
-            ]
-        nameConstants = [ClassInfo 9, Utf8Info name]
-        nakedClassFile = ClassFile {
-            constantPool = baseConstants ++ nameConstants,
-            accessFlags = accessPublic,
-            thisClass = 8,
-            superClass = 1,
-            fields = [],
-            methods = [],
-            attributes = []
-        }
-    in
-        foldr methodBuilder (foldr fieldBuilder nakedClassFile fields) methods
-        
-        
-
-fieldBuilder :: ClassFileBuilder VariableDeclaration
-fieldBuilder (VariableDeclaration datatype name _) input = let
-        baseIndex = 1 + length (constantPool input)
-        constants = [
-                FieldRefInfo (fromIntegral (thisClass input)) (fromIntegral (baseIndex + 1)),
-                NameAndTypeInfo (fromIntegral (baseIndex + 2)) (fromIntegral (baseIndex + 3)),
-                Utf8Info name,
-                Utf8Info (datatypeDescriptor datatype)
-            ]
-        field = MemberInfo {
-            memberAccessFlags = accessPublic,
-            memberNameIndex = (fromIntegral (baseIndex + 2)),
-            memberDescriptorIndex = (fromIntegral (baseIndex + 3)),
-            memberAttributes = []
-            }
-    in
-        input {
-            constantPool = (constantPool input) ++ constants,
-            fields = (fields input) ++ [field]
-        }
-
-methodBuilder :: ClassFileBuilder MethodDeclaration
-methodBuilder (MethodDeclaration returntype name parameters statement) input = let
-        baseIndex = 1 + length (constantPool input)
-        constants = [
-                FieldRefInfo (fromIntegral (thisClass input)) (fromIntegral (baseIndex + 1)),
-                NameAndTypeInfo (fromIntegral (baseIndex + 2)) (fromIntegral (baseIndex + 3)),
-                Utf8Info name,
-                Utf8Info (methodDescriptor (MethodDeclaration returntype name parameters (Block [])))
-            ]
-        --code = assembleByteCode statement
-        method = MemberInfo {
-            memberAccessFlags = accessPublic,
-            memberNameIndex = (fromIntegral (baseIndex + 2)),
-            memberDescriptorIndex = (fromIntegral (baseIndex + 3)),
-            memberAttributes = [
-                   CodeAttribute {
-                        attributeMaxStack = 420,
-                        attributeMaxLocals = 420,
-                        attributeCode = [Opiadd]
-                    }
-                ]
-            }
-    in
-        input {
-            constantPool = (constantPool input) ++ constants,
-            methods = (fields input) ++ [method]
-        }
-
-type Assembler a = a -> ([ConstantInfo], [Operation]) -> ([ConstantInfo], [Operation])
-
-returnOperation :: DataType -> Operation
-returnOperation dtype
-    | elem dtype ["int", "char", "boolean"] = Opireturn
-    | otherwise                             = Opareturn
-
-binaryOperation :: BinaryOperator -> Operation
-binaryOperation Addition        = Opiadd
-binaryOperation Subtraction     = Opisub
-binaryOperation Multiplication  = Opimul
-binaryOperation Division        = Opidiv
-binaryOperation BitwiseAnd      = Opiand
-binaryOperation BitwiseOr       = Opior
-binaryOperation BitwiseXor      = Opixor
-
-assembleMethod :: Assembler MethodDeclaration
-assembleMethod (MethodDeclaration _ _ _ (Block statements)) (constants, ops) =
-    foldr assembleStatement (constants, ops) statements
-
-assembleStatement :: Assembler Statement
-assembleStatement (TypedStatement stype (Return expr)) (constants, ops) = case expr of
-    Nothing -> (constants, ops ++ [Opreturn])
-    Just expr -> let
-            (expr_constants, expr_ops) = assembleExpression expr (constants, ops)
-        in  
-            (expr_constants, expr_ops ++ [returnOperation stype])
-
-assembleExpression :: Assembler Expression
-assembleExpression (TypedExpression _ (BinaryOperation op a b)) (constants, ops)
-    | elem op [Addition, Subtraction, Multiplication, Division, BitwiseAnd, BitwiseOr, BitwiseXor] = let
-            (aConstants, aOps) = assembleExpression a (constants, ops)
-            (bConstants, bOps) = assembleExpression b (aConstants, aOps)
-        in
-            (bConstants, bOps ++ [binaryOperation op])
-assembleExpression (TypedExpression _ (CharacterLiteral literal)) (constants, ops) = 
-    (constants, ops ++ [Opsipush (fromIntegral (ord literal))])
-assembleExpression (TypedExpression _ (BooleanLiteral literal)) (constants, ops) = 
-    (constants, ops ++ [Opsipush (if literal then 1 else 0)])
-assembleExpression (TypedExpression _ (IntegerLiteral literal)) (constants, ops)
-    | literal <= 32767 && literal >= -32768 = (constants, ops ++ [Opsipush (fromIntegral literal)])
-    | otherwise = (constants ++ [IntegerInfo (fromIntegral literal)], ops ++ [Opldc_w (fromIntegral (1 + length constants))])
-assembleExpression (TypedExpression _ NullLiteral) (constants, ops) = 
-    (constants, ops ++ [Opaconst_null])
-assembleExpression (TypedExpression etype (UnaryOperation Not expr)) (constants, ops) = let
-        (exprConstants, exprOps) = assembleExpression expr (constants, ops)
-        newConstant = fromIntegral (1 + length exprConstants)
-    in case etype of
-        "int" -> (exprConstants ++ [IntegerInfo 0x7FFFFFFF], exprOps ++ [Opldc_w newConstant, Opixor])
-        "char" -> (exprConstants, exprOps ++ [Opsipush 0xFFFF, Opixor])
-        "boolean" -> (exprConstants, exprOps ++ [Opsipush 0x01, Opixor])
-assembleExpression (TypedExpression _ (UnaryOperation Minus expr)) (constants, ops) = let
-        (exprConstants, exprOps) = assembleExpression expr (constants, ops)
-    in
-        (exprConstants, exprOps ++ [Opineg])

src/ByteCode/Util.hs

@@ -0,0 +1,292 @@
+module ByteCode.Util where
+
+import Data.Int
+import Ast
+import ByteCode.ClassFile
+import Data.List
+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 (FieldVariable name)) = TypedExpression dtype (FieldVariable name)
+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)
+
+methodDescriptor :: MethodDeclaration -> String
+methodDescriptor (MethodDeclaration returntype _ parameters _) = let
+        parameter_types = [datatype | ParameterDeclaration datatype _ <- parameters]
+    in
+        "("
+        ++ concatMap datatypeDescriptor parameter_types
+        ++ ")"
+        ++ datatypeDescriptor returntype
+
+methodDescriptorFromParamlist :: [Expression] -> String -> String
+methodDescriptorFromParamlist parameters returntype = let
+        parameter_types = [datatype | TypedExpression datatype _ <- parameters]
+    in
+        "("
+        ++ concatMap datatypeDescriptor parameter_types
+        ++ ")"
+        ++ datatypeDescriptor returntype
+
+-- recursively parses a given type signature into a list of parameter types and the method return type.
+-- 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" = "Z"
+datatypeDescriptor x = "L" ++ x ++ ";"
+
+memberInfoDescriptor :: [ConstantInfo] -> MemberInfo -> String
+memberInfoDescriptor constants MemberInfo { memberDescriptorIndex = descriptorIndex } = let
+            descriptor = constants !! (fromIntegral descriptorIndex - 1)
+        in case descriptor of
+            Utf8Info descriptorText -> descriptorText
+            _ -> "Invalid Item at Constant pool index " ++ show descriptorIndex
+
+memberInfoName :: [ConstantInfo] -> MemberInfo -> String
+memberInfoName constants MemberInfo { memberNameIndex = nameIndex } = let
+            name = constants !! (fromIntegral nameIndex - 1)
+        in case name of
+            Utf8Info nameText -> nameText
+            _ -> "Invalid Item at Constant pool index " ++ show nameIndex
+
+returnOperation :: DataType -> Operation
+returnOperation dtype
+    | dtype `elem` ["int", "char", "boolean"] = Opireturn
+    | otherwise                               = Opareturn
+
+binaryOperation :: BinaryOperator -> Operation
+binaryOperation Addition       = Opiadd
+binaryOperation Subtraction    = Opisub
+binaryOperation Multiplication = Opimul
+binaryOperation Division       = Opidiv
+binaryOperation Modulo         = Opirem
+binaryOperation BitwiseAnd     = Opiand
+binaryOperation BitwiseOr      = Opior
+binaryOperation BitwiseXor     = Opixor
+binaryOperation And            = Opiand
+binaryOperation Or             = Opior
+
+comparisonOperation :: BinaryOperator -> Word16 -> Operation
+comparisonOperation CompareEqual          branchLocation = Opif_icmpeq branchLocation
+comparisonOperation CompareNotEqual       branchLocation = Opif_icmpne branchLocation
+comparisonOperation CompareLessThan       branchLocation = Opif_icmplt branchLocation
+comparisonOperation CompareLessOrEqual    branchLocation = Opif_icmple branchLocation
+comparisonOperation CompareGreaterThan    branchLocation = Opif_icmpgt branchLocation
+comparisonOperation CompareGreaterOrEqual branchLocation = Opif_icmpge branchLocation
+
+comparisonOffset :: Operation -> Maybe Int
+comparisonOffset (Opif_icmpeq offset) = Just $ fromIntegral offset
+comparisonOffset (Opif_icmpne offset) = Just $ fromIntegral offset
+comparisonOffset (Opif_icmplt offset) = Just $ fromIntegral offset
+comparisonOffset (Opif_icmple offset) = Just $ fromIntegral offset
+comparisonOffset (Opif_icmpgt offset) = Just $ fromIntegral offset
+comparisonOffset (Opif_icmpge offset) = Just $ fromIntegral offset
+comparisonOffset anything_else = 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)
+
+findClassIndex :: [ConstantInfo] -> String -> Maybe Int
+findClassIndex constants name = let
+        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))
+                classNameIndices
+        desiredClassIndex = find (\(index, className) -> className == name) classNames
+    in case desiredClassIndex of
+        Just (index, _) -> Just index
+        Nothing -> Nothing
+
+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, constants!!(fromIntegral classIndex - 1), constants!!(fromIntegral nameTypeIndex - 1))
+                | (index, MethodRefInfo classIndex nameTypeIndex) <- zip [1..] constants
+            ]
+
+        fieldsClassNameType = map (\(index, nameInfo, nameTypeInfo) -> case (nameInfo, nameTypeInfo) of
+            (ClassInfo nameIndex, NameAndTypeInfo fnameIndex ftypeIndex) -> (index, (constants!!(fromIntegral nameIndex - 1), constants!!(fromIntegral fnameIndex - 1), constants!!(fromIntegral ftypeIndex - 1)))
+            something_else -> error ("Expected Class and NameType info, but got: " ++ show nameInfo ++ " and " ++ show nameTypeInfo))
+                fieldsClassAndNT
+
+        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))
+                fieldsClassNameType
+    in
+        fieldsResolved
+
+-- same as findClassIndex, but inserts a new entry into constant pool if not existing
+getClassIndex :: [ConstantInfo] -> String -> ([ConstantInfo], Int)
+getClassIndex constants name = case findClassIndex constants name of
+    Just index -> (constants, index)
+    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)
+getFieldIndex constants (cname, fname, ftype) = case findMemberIndex constants (cname, fname, ftype) of
+    Just index -> (constants, index)
+    Nothing -> let
+            (constantsWithClass, classIndex) = getClassIndex constants cname
+            baseIndex = 1 + length constantsWithClass
+        in
+            (constantsWithClass ++ [
+                FieldRefInfo (fromIntegral classIndex) (fromIntegral (baseIndex + 1)),
+                NameAndTypeInfo (fromIntegral (baseIndex + 2)) (fromIntegral (baseIndex + 3)),
+                Utf8Info fname,
+                Utf8Info (datatypeDescriptor ftype)
+            ], baseIndex)
+
+getMethodIndex :: [ConstantInfo] -> (String, String, String) -> ([ConstantInfo], Int)
+getMethodIndex constants (cname, mname, mtype) = case findMemberIndex constants (cname, mname, mtype) of
+    Just index -> (constants, index)
+    Nothing -> let
+            (constantsWithClass, classIndex) = getClassIndex constants cname
+            baseIndex = 1 + length constantsWithClass
+        in
+            (constantsWithClass ++ [
+                MethodRefInfo (fromIntegral classIndex) (fromIntegral (baseIndex + 1)),
+                NameAndTypeInfo (fromIntegral (baseIndex + 2)) (fromIntegral (baseIndex + 3)),
+                Utf8Info mname,
+                Utf8Info mtype
+            ], baseIndex)
+
+findMemberIndex :: [ConstantInfo] -> (String, String, String) -> Maybe Int
+findMemberIndex constants (cname, fname, ftype) = let
+        allMembers = getKnownMembers constants
+        desiredMember = find (\(index, (c, f, ft)) -> (c, f, ft) == (cname, fname, ftype)) allMembers
+    in
+        fmap (\(index, _) -> index) desiredMember
+
+injectDefaultConstructor :: [MethodDeclaration] -> [MethodDeclaration]
+injectDefaultConstructor pre
+    | any (\(MethodDeclaration _ name _ _) -> name == "<init>") pre = pre
+    | otherwise = pre ++ [MethodDeclaration "void" "<init>" [] (TypedStatement "void" (Block []))]
+
+injectFieldInitializers :: String -> [VariableDeclaration] -> [MethodDeclaration] -> [MethodDeclaration]
+injectFieldInitializers classname vars pre = let
+        initializers = mapMaybe (\(variable) -> case variable of
+                VariableDeclaration dtype name (Just initializer) -> Just (
+                        TypedStatement dtype (
+                            StatementExpressionStatement (
+                                TypedStatementExpression dtype (
+                                    Assignment
+                                        (TypedExpression dtype (BinaryOperation NameResolution (TypedExpression classname (LocalVariable "this")) (TypedExpression dtype (FieldVariable name))))
+                                        initializer
+                                    )
+                                )
+                            )
+                        )
+                otherwise -> Nothing
+            ) vars
+    in
+        map (\method -> case method of
+                MethodDeclaration "void" "<init>" params (TypedStatement "void" (Block statements)) -> MethodDeclaration "void" "<init>" params (TypedStatement "void" (Block (initializers ++ statements)))
+                _ -> 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

@@ -1,8 +1,32 @@
 module Main where
 
-import Example
 import Typecheck
+import Parser.Lexer (alexScanTokens)
+import Parser.JavaParser
+import ByteCode.Builder
+import ByteCode.ClassFile
+import Data.ByteString (pack, writeFile)
+import System.Environment
+import System.FilePath.Posix (takeDirectory)
 
 main = do
-    Example.runTypeCheck
+    args <- getArgs
+    let filename = if null args
+                   then error "Missing filename, I need to know what to compile"
+                   else head args
+    let outputDirectory = takeDirectory filename
+    print ("Compiling " ++ filename)
+    file <- readFile filename
+
+    let untypedAST = parse $ alexScanTokens file
+    let typedAST = typeCheckCompilationUnit untypedAST
+    let assembledClasses = map (`classBuilder` emptyClassFile) typedAST
+
+    mapM_ (\classFile -> let
+            fileContent = pack (serialize classFile)
+            fileName = outputDirectory ++ "/" ++ className classFile ++ ".class"
+        in Data.ByteString.writeFile fileName fileContent
+            ) assembledClasses
+
+
 

src/Typecheck.hs

@@ -9,25 +9,46 @@ typeCheckCompilationUnit classes = map (`typeCheckClass` classes) classes
 typeCheckClass :: Class -> [Class] -> Class
 typeCheckClass (Class className methods fields) classes =
     let
-        -- Create a symbol table from class fields and method entries
+        -- Fields and methods dont need to be added to the symtab because they are looked upon automatically under "this" 
-        -- TODO: Maybe remove method entries from the symbol table?
+        -- if its not a declared local variable. Also shadowing wouldnt be possible then.
-        methodEntries = [(methodName, className) | MethodDeclaration _ methodName _ _ <- methods]
+        initalSymTab = [("this", className)]
-        initalSymTab = ("this", className) : methodEntries
         checkedMethods = map (\method -> typeCheckMethodDeclaration method initalSymTab classes) methods
-    in Class className checkedMethods fields
+        checkedFields = map (\field -> typeCheckVariableDeclaration field initalSymTab classes) fields
+    in Class className checkedMethods checkedFields
 
 typeCheckMethodDeclaration :: MethodDeclaration -> [(Identifier, DataType)] -> [Class] -> MethodDeclaration
-typeCheckMethodDeclaration (MethodDeclaration retType name params body) classFields classes =
+typeCheckMethodDeclaration (MethodDeclaration retType name params body) symtab classes =
     let
-        -- Combine class fields with method parameters to form the initial symbol table for the method
         methodParams = [(identifier, dataType) | ParameterDeclaration dataType identifier <- params]
-        initialSymtab = classFields ++ methodParams
+        initialSymtab = ("thisMeth", retType) : symtab ++ methodParams
         checkedBody = typeCheckStatement body initialSymtab classes
         bodyType = getTypeFromStmt checkedBody
-        -- Check if the type of the body matches the declared return type
+    in if bodyType == retType || (bodyType == "void" && retType == "void") || (bodyType == "null" && isObjectType retType) || isSubtype bodyType retType classes
-    in if bodyType == retType || (bodyType == "void" && retType == "void") || (bodyType == "null" && isObjectType retType)
        then MethodDeclaration retType name params checkedBody
-       else error $ "Return type mismatch in method " ++ name ++ ": expected " ++ retType ++ ", found " ++ bodyType
+       else error $ "Method Declaration: Return type mismatch in method " ++ name ++ ": expected " ++ retType ++ ", found " ++ bodyType
+
+typeCheckVariableDeclaration :: VariableDeclaration -> [(Identifier, DataType)] -> [Class] -> VariableDeclaration
+typeCheckVariableDeclaration (VariableDeclaration dataType identifier maybeExpr) symtab classes =
+    let
+        -- Ensure the type is valid (either a primitive type or a valid class name)
+        validType = dataType `elem` ["int", "boolean", "char"] || isUserDefinedClass dataType classes
+        -- Ensure no redefinition in the same scope
+        redefined = any ((== identifier) . snd) symtab
+        -- 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 checkedExprWithType
+            | t /= dataType -> error $ "Type mismatch in declaration of '" ++ identifier ++ "': expected " ++ dataType ++ ", found " ++ t
+            | otherwise -> VariableDeclaration dataType identifier checkedExprWithType
+        (_, _, Nothing) -> VariableDeclaration dataType identifier checkedExprWithType
+
 
 -- ********************************** Type Checking: Expressions **********************************
 
@@ -46,8 +67,9 @@ typeCheckExpression (Reference id) symtab classes =
           in case classDetails of
             Just (Class _ _ fields) ->
               let fieldTypes = [dt | VariableDeclaration dt fieldId _ <- fields, fieldId == id]
+              -- this case only happens when its a field of its own class so the implicit this will be converted to explicit this
               in case fieldTypes of
-                [fieldType] -> TypedExpression fieldType (FieldVariable id)
+                [fieldType] -> TypedExpression fieldType (BinaryOperation NameResolution (TypedExpression className (LocalVariable "this")) (TypedExpression fieldType (FieldVariable id)))
                 [] -> error $ "Field '" ++ id ++ "' not found in class '" ++ className ++ "'"
                 _ -> error $ "Ambiguous reference to field '" ++ id ++ "' in class '" ++ className ++ "'"
             Nothing -> error $ "Class '" ++ className ++ "' not found for 'this'"
@@ -107,35 +129,50 @@ 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 _) ->
-      -- Constructor needs the same name as the class
+      -- Find constructor matching the class name with void return type
-      case find (\(MethodDeclaration retType name params _) -> name == className && retType == className) methods of
+      case find (\(MethodDeclaration _ name params _) -> name == "<init>") methods of
-        Nothing -> error $ "No valid constructor found for class '" ++ className ++ "'."
+        -- If no constructor is found, assume standard constructor with no parameters
+        Nothing ->
+          if null args then
+            TypedStatementExpression className (ConstructorCall className args)
+          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
-            expectedTypes = [dataType | ParameterDeclaration dataType _ <- params]
+                    in if getTypeFromExpr argTyped == "null" && isObjectType paramType
-            argTypes = map getTypeFromExpr args'
+                      then TypedExpression paramType NullLiteral
-            -- Check if the types of the provided arguments match the expected types
+                      else argTyped
-            typeMatches = zipWith (\expected actual -> if expected == actual then Nothing else Just (expected, actual)) expectedTypes argTypes
+                  ) args params
-            mismatchErrors = map (\(exp, act) -> "Expected type '" ++ exp ++ "', found '" ++ act ++ "'.") (catMaybes typeMatches)
+              expectedTypes = [dataType | ParameterDeclaration dataType _ <- params]
+              argTypes = map getTypeFromExpr args'
+              typeMatches = zipWith
+                  (\expType argType -> (expType == argType || (argType == "null" && isObjectType expType), expType, argType))
+                  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
@@ -145,20 +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."
@@ -203,16 +246,22 @@ typeCheckStatementExpression (PreDecrement expr) symtab classes =
 
 typeCheckStatement :: Statement -> [(Identifier, DataType)] -> [Class] -> Statement
 typeCheckStatement (If cond thenStmt elseStmt) symtab classes =
-  let cond' = typeCheckExpression cond symtab classes
+  let
-      thenStmt' = typeCheckStatement thenStmt symtab classes
+    cond' = typeCheckExpression cond symtab classes
-      elseStmt' = case elseStmt of
+    thenStmt' = typeCheckStatement thenStmt symtab classes
-        Just stmt -> Just (typeCheckStatement stmt symtab classes)
+    elseStmt' = fmap (\stmt -> typeCheckStatement stmt symtab classes) elseStmt
-        Nothing   -> Nothing
+
-   in if getTypeFromExpr cond' == "boolean"
+    thenType = getTypeFromStmt thenStmt'
-        then
+    elseType = maybe "void" getTypeFromStmt elseStmt'
-          TypedStatement (getTypeFromStmt thenStmt') (If cond' thenStmt' elseStmt')
+
-        else
+    ifType = if thenType == "void" || elseType == "void"
-          error "If condition must be of type boolean"
+             then "void"
+             else unifyReturnTypes thenType elseType
+
+  in if getTypeFromExpr cond' == "boolean"
+       then TypedStatement ifType (If cond' thenStmt' elseStmt')
+       else error "If condition must be of type boolean"
+
 
 typeCheckStatement (LocalVariableDeclaration (VariableDeclaration dataType identifier maybeExpr)) symtab classes =
     -- Check for redefinition in the current scope
@@ -222,14 +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
@@ -242,37 +295,50 @@ typeCheckStatement (While cond stmt) symtab classes =
 typeCheckStatement (Block statements) symtab classes =
     let
         processStatements (accSts, currentSymtab, types) stmt =
-            let
+            case stmt of
-                checkedStmt = typeCheckStatement stmt currentSymtab classes
-                stmtType = getTypeFromStmt checkedStmt
-            in case stmt of
                 LocalVariableDeclaration (VariableDeclaration dataType identifier maybeExpr) ->
                     let
+                        alreadyDefined = any (\(id, _) -> id == identifier) currentSymtab
+                        newSymtab = if alreadyDefined
+                                    then error ("Variable " ++ identifier ++ " already defined in this scope.")
+                                    else (identifier, dataType) : currentSymtab
                         checkedExpr = fmap (\expr -> typeCheckExpression expr currentSymtab classes) maybeExpr
-                        newSymtab = (identifier, dataType) : currentSymtab
+                        checkedStmt = typeCheckStatement stmt newSymtab classes
                     in (accSts ++ [checkedStmt], newSymtab, types)
 
-                If {} -> (accSts ++ [checkedStmt], currentSymtab, if stmtType /= "void" then types ++ [stmtType] else types)
+                _ ->
-                While _ _ -> (accSts ++ [checkedStmt], currentSymtab, if stmtType /= "void" then types ++ [stmtType] else types)
+                    let
-                Return _ -> (accSts ++ [checkedStmt], currentSymtab, if stmtType /= "void" then types ++ [stmtType] else types)
+                        checkedStmt = typeCheckStatement stmt currentSymtab classes
-                Block _ -> (accSts ++ [checkedStmt], currentSymtab, if stmtType /= "void" then types ++ [stmtType] else types)
+                        stmtType = getTypeFromStmt checkedStmt
-                _ -> (accSts ++ [checkedStmt], currentSymtab, types)
+                    in case stmt of
+                        If {} -> (accSts ++ [checkedStmt], currentSymtab, if stmtType /= "void" then types ++ [stmtType] else types)
+                        While _ _ -> (accSts ++ [checkedStmt], currentSymtab, if stmtType /= "void" then types ++ [stmtType] else types)
+                        Return _ -> (accSts ++ [checkedStmt], currentSymtab, if stmtType /= "void" then types ++ [stmtType] else types)
+                        Block _ -> (accSts ++ [checkedStmt], currentSymtab, if stmtType /= "void" then types ++ [stmtType] else types)
+                        _ -> (accSts ++ [checkedStmt], currentSymtab, types)
 
         -- Initial accumulator: empty statements list, initial symbol table, empty types list
         (checkedStatements, finalSymtab, collectedTypes) = foldl processStatements ([], symtab, []) statements
 
-        -- Determine the block's type: unify all collected types, default to "Void" if none
+        -- Determine the block's type: unify all collected types, default to "void" if none (UpperBound)
         blockType = if null collectedTypes then "void" else foldl1 unifyReturnTypes collectedTypes
 
     in TypedStatement blockType (Block checkedStatements)
 
+
 typeCheckStatement (Return expr) symtab classes =
-  let expr' = case expr of
+  let methodReturnType = fromMaybe (error "Method return type not found in symbol table") (lookup "thisMeth" symtab)
-        Just e  -> Just (typeCheckExpression e symtab classes)
+      expr' = case expr of
+        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
-   in case expr' of
+      returnType = maybe "void" getTypeFromExpr expr'
-        Just e' -> TypedStatement (getTypeFromExpr e') (Return (Just e'))
+  in if returnType == methodReturnType || isSubtype returnType methodReturnType classes
-        Nothing -> TypedStatement "void" (Return Nothing)
+       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
@@ -280,6 +346,17 @@ typeCheckStatement (StatementExpressionStatement stmtExpr) symtab classes =
 
 -- ********************************** Type Checking: Helpers **********************************
 
+isSubtype :: DataType -> DataType -> [Class] -> Bool
+isSubtype subType superType classes
+  | subType == superType = True
+  | subType == "null" && isObjectType superType = True
+  | superType == "Object" && isObjectType subType = True
+  | superType == "Object" && isUserDefinedClass subType classes = True
+  | otherwise = False
+
+isUserDefinedClass :: DataType -> [Class] -> Bool
+isUserDefinedClass dt classes = dt `elem` map (\(Class name _ _) -> name) classes
+
 isObjectType :: DataType -> Bool
 isObjectType dt = dt /= "int" && dt /= "boolean" && dt /= "char"
 
@@ -297,8 +374,10 @@ getTypeFromStmtExpr _ = error "Untyped statement expression found where typed wa
 
 unifyReturnTypes :: DataType -> DataType -> DataType
 unifyReturnTypes dt1 dt2
-    | dt1 == dt2 = dt1
+  | dt1 == dt2 = dt1
-    | otherwise  = "Object"
+  | dt1 == "null" = dt2
+  | dt2 == "null" = dt1
+  | otherwise = "Object"
 
 resolveResultType :: DataType -> DataType -> DataType
 resolveResultType "char" "char" = "char"
@@ -319,7 +398,7 @@ checkBitwiseOperation :: BinaryOperator -> Expression -> Expression -> DataType
 checkBitwiseOperation op expr1' expr2' type1 type2
   | type1 == "int" && type2 == "int" =
       TypedExpression "int" (BinaryOperation op expr1' expr2')
-  | otherwise = error $ "Bitwise operation " ++ show op ++ " requires operands of type int"
+  | otherwise = error $ "Bitwise operation " ++ show op ++ " requires operands of type int or char"
 
 checkComparisonOperation :: BinaryOperator -> Expression -> Expression -> DataType -> DataType -> Expression
 checkComparisonOperation op expr1' expr2' type1 type2