diff --git a/.gitignore b/.gitignore
index d0ab5db..1daddd6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,9 @@ dist-newstyle
 *.x
 *.bak
 src/Grammar
+
+language
+llvm.ll
 /language
 .vscode/
 
diff --git a/Grammar.cf b/Grammar.cf
index b258446..0b4785f 100644
--- a/Grammar.cf
+++ b/Grammar.cf
@@ -1,15 +1,25 @@
+Program. Program ::= [Bind];
 
+EId.  Exp3 ::= Ident;
+EInt. Exp3 ::= Integer;
+EAnn. Exp3  ::= "(" Exp ":" Type ")";
+ELet. Exp3 ::= "let" Bind "in" Exp; 
+EApp. Exp2 ::= Exp2 Exp3;
+EAdd. Exp1 ::= Exp1 "+" Exp2;
+EAbs. Exp  ::= "\\" Ident ":" Type "." Exp;
 
-Program. Program ::= "main" "=" Exp ;
+Bind. Bind ::= Ident ":" Type ";"
+               Ident [Ident] "=" Exp;
 
-EId.  Exp3 ::= Ident   ;
-EInt. Exp3 ::= Integer ;
-EApp. Exp2 ::= Exp2 Exp3 ;
-EAdd. Exp1 ::= Exp1 "+" Exp2 ;
-EAbs. Exp  ::= "\\" Ident "->" Exp ;
+separator Bind ";";
+separator Ident "";
 
-coercions Exp 3 ;
+coercions Exp 3;
 
-comment "--" ;
-comment "{-" "-}" ;
+TInt. Type1 ::= "Int" ;
+TPol. Type1 ::= Ident ;
+TFun. Type  ::= Type1 "->" Type ;
+coercions Type 1 ;
 
+comment "--";
+comment "{-" "-}";
diff --git a/Makefile b/Makefile
index 16b753d..e63a1e6 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 .PHONY : sdist clean
 
 language : src/Grammar/Test
-	cabal install --installdir=.
+	cabal install --installdir=. --overwrite-policy=always
 
 src/Grammar/Test.hs src/Grammar/Lex.x src/Grammar/Par.y : Grammar.cf
 	bnfc -o src -d $<
@@ -22,4 +22,16 @@ clean :
 	rm -r src/Grammar
 	rm language
 
+test :
+	./language ./sample-programs/basic-1
+	./language ./sample-programs/basic-2
+	./language ./sample-programs/basic-3
+	./language ./sample-programs/basic-4
+	./language ./sample-programs/basic-5
+	./language ./sample-programs/basic-5
+	./language ./sample-programs/basic-6
+	./language ./sample-programs/basic-7
+	./language ./sample-programs/basic-8
+	./language ./sample-programs/basic-9
+
 # EOF
diff --git a/cabal.project.local b/cabal.project.local
new file mode 100644
index 0000000..0432756
--- /dev/null
+++ b/cabal.project.local
@@ -0,0 +1,2 @@
+ignore-project: False
+tests: True
diff --git a/language.cabal b/language.cabal
index 5734655..8b958a5 100644
--- a/language.cabal
+++ b/language.cabal
@@ -1,4 +1,4 @@
-cabal-version:      3.0
+cabal-version:      3.4
 
 name:               language
 
@@ -12,26 +12,34 @@ build-type:         Simple
 
 extra-doc-files:    CHANGELOG.md
 
+
 extra-source-files:
   Grammar.cf
 
 
 common warnings
-    ghc-options: -Wall
+    ghc-options: -W
 
 executable language
     import:           warnings
 
     main-is:          Main.hs
-
+    
     other-modules:
       Grammar.Abs
       Grammar.Lex
       Grammar.Par
       Grammar.Print
       Grammar.Skel
-      Interpreter
-
+      Grammar.ErrM
+      LambdaLifter
+      Auxiliary
+      Renamer
+      TypeChecker
+      TypeCheckerIr
+--      Interpreter
+      Compiler
+      LlvmIr
     hs-source-dirs:   src
 
     build-depends:    
@@ -40,5 +48,5 @@ executable language
       , containers
       , either
       , array
-
+      , extra
     default-language: GHC2021
diff --git a/sample-programs/basic-1 b/sample-programs/basic-1
new file mode 100644
index 0000000..f0cdcc4
--- /dev/null
+++ b/sample-programs/basic-1
@@ -0,0 +1,21 @@
+
+-- tripplemagic : Int -> Int -> Int -> Int;
+-- tripplemagic x y z = ((\x:Int. x+x) x) + y + z;
+-- main : Int;
+-- main = tripplemagic ((\x:Int. x+x+3) ((\x:Int. x) 2)) 5 3
+-- answer: 22
+
+-- apply : (Int -> Int) -> Int -> Int;
+-- apply f x = f x;
+-- main : Int;
+-- main = apply (\x : Int . x + 5) 5
+-- answer: 10
+
+apply : (Int -> Int -> Int) -> Int -> Int -> Int;
+apply f x y = f x y;
+krimp: Int -> Int -> Int;
+krimp x y = x + y;
+main : Int;
+main = apply (krimp) 2 3;
+-- answer: 5
+
diff --git a/shell.nix b/shell.nix
index 0c7624a..0af8c7b 100644
--- a/shell.nix
+++ b/shell.nix
@@ -1,12 +1,12 @@
 let
-  pkgs = import <nixpkgs> { }; # pin the channel to ensure reproducibility!
+  pkgs = import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/747927516efcb5e31ba03b7ff32f61f6d47e7d87.zip") { }; # pin the channel to ensure reproducibility!
 in
 pkgs.haskellPackages.developPackage {
   root = ./.;
   withHoogle = true;
   modifier = drv:
   pkgs.haskell.lib.addBuildTools drv (
-    (with pkgs; [ hlint haskell-language-server ghc jasmin ])
+    (with pkgs; [ hlint haskell-language-server ghc jasmin llvmPackages_15.libllvm])
     ++
     (with pkgs.haskellPackages; [ 
       cabal-install
diff --git a/src/Auxiliary.hs b/src/Auxiliary.hs
new file mode 100644
index 0000000..735d804
--- /dev/null
+++ b/src/Auxiliary.hs
@@ -0,0 +1,21 @@
+{-# LANGUAGE LambdaCase #-}
+module Auxiliary (module Auxiliary) where
+import           Control.Monad.Error.Class (liftEither)
+import           Control.Monad.Except      (MonadError)
+import           Data.Either.Combinators   (maybeToRight)
+
+snoc :: a -> [a] -> [a]
+snoc x xs = xs ++ [x]
+
+maybeToRightM :: MonadError l m => l -> Maybe r -> m r
+maybeToRightM err = liftEither . maybeToRight err
+
+mapAccumM :: Monad m => (s -> a -> m (s, b)) -> s -> [a] -> m (s, [b])
+mapAccumM f = go
+  where
+    go acc = \case
+      [] -> pure (acc, [])
+      x:xs -> do
+        (acc', x') <- f acc x
+        (acc'', xs') <- go acc' xs
+        pure (acc'', x':xs')
diff --git a/src/Compiler.hs b/src/Compiler.hs
index e69de29..fd6b6bc 100644
--- a/src/Compiler.hs
+++ b/src/Compiler.hs
@@ -0,0 +1,266 @@
+{-# LANGUAGE LambdaCase        #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+module Compiler (compile) where
+
+import           Auxiliary           (snoc)
+import           Control.Monad.State (StateT, execStateT, gets, modify)
+import           Data.Map            (Map)
+import qualified Data.Map            as Map
+import           Data.Tuple.Extra    (dupe, first, second)
+import           Grammar.ErrM        (Err)
+import           LlvmIr              (LLVMIr (..), LLVMType (..),
+                                      LLVMValue (..), Visibility (..),
+                                      llvmIrToString)
+import           TypeChecker         (partitionType)
+import           TypeCheckerIr
+
+-- | The record used as the code generator state
+data CodeGenerator = CodeGenerator
+    { instructions  :: [LLVMIr]
+    , functions     :: Map Id FunctionInfo
+    , variableCount :: Integer
+    }
+
+-- | A state type synonym
+type CompilerState a = StateT CodeGenerator Err a
+
+data FunctionInfo = FunctionInfo
+    { numArgs   :: Int
+    , arguments :: [Id]
+    }
+
+-- | Adds a instruction to the CodeGenerator state
+emit :: LLVMIr -> CompilerState ()
+emit l = modify $ \t -> t { instructions = snoc l $ instructions t }
+
+-- | Increases the variable counter in the CodeGenerator state
+increaseVarCount :: CompilerState ()
+increaseVarCount = modify $ \t -> t { variableCount = variableCount t + 1 }
+
+-- | Returns the variable count from the CodeGenerator state
+getVarCount :: CompilerState Integer
+getVarCount = gets variableCount
+
+-- | Increases the variable count and returns it from the CodeGenerator state
+getNewVar :: CompilerState Integer
+getNewVar = increaseVarCount >> getVarCount
+
+-- | Produces a map of functions infos from a list of binds,
+-- which contains useful data for code generation.
+getFunctions :: [Bind] -> Map Id FunctionInfo
+getFunctions bs = Map.fromList $ map go bs
+  where
+    go (Bind id args _) =
+        (id, FunctionInfo { numArgs=length args, arguments=args })
+
+
+
+initCodeGenerator :: [Bind] -> CodeGenerator
+initCodeGenerator scs = CodeGenerator { instructions = defaultStart
+                                      , functions = getFunctions scs
+                                      , variableCount = 0
+                                      }
+
+-- | Compiles an AST and produces a LLVM Ir string.
+-- An easy way to actually "compile" this output is to
+-- Simply pipe it to lli
+compile :: Program -> Err String
+compile (Program scs) = do
+    let codegen = initCodeGenerator scs
+    llvmIrToString . instructions <$> execStateT (compileScs scs) codegen
+
+compileScs :: [Bind] -> CompilerState ()
+compileScs []                             = pure ()
+compileScs (Bind (name, t) args exp : xs) = do
+    emit $ UnsafeRaw "\n"
+    emit . Comment $ show name <> ": " <> show exp
+    let args' = map (second type2LlvmType) args
+    emit $ Define (type2LlvmType t_return) name args'
+    functionBody <- exprToValue exp
+    if name == "main"
+        then mapM_ emit $ mainContent functionBody
+        else emit $ Ret I64 functionBody
+    emit DefineEnd
+    modify $ \s -> s { variableCount = 0 }
+    compileScs xs
+  where
+    t_return = snd $ partitionType (length args) t
+
+mainContent :: LLVMValue -> [LLVMIr]
+mainContent var =
+    [ UnsafeRaw $
+        "call i32 (ptr, ...) @printf(ptr noundef @.str, i64 noundef " <> show var <> ")\n"
+    , -- , SetVariable (Ident "p") (Icmp LLEq I64 (VInteger 2) (VInteger 2))
+      -- , BrCond (VIdent (Ident "p")) (Ident "b_1") (Ident "b_2")
+      -- , Label (Ident "b_1")
+      -- , UnsafeRaw
+      --     "call i32 (ptr, ...) @printf(ptr noundef @.str, i64 noundef 1)\n"
+      -- , Br (Ident "end")
+      -- , Label (Ident "b_2")
+      -- , UnsafeRaw
+      --     "call i32 (ptr, ...) @printf(ptr noundef @.str, i64 noundef 2)\n"
+      -- , Br (Ident "end")
+      -- , Label (Ident "end")
+      Ret I64 (VInteger 0)
+    ]
+
+defaultStart :: [LLVMIr]
+defaultStart = [ UnsafeRaw "@.str = private unnamed_addr constant [3 x i8] c\"%i\n\", align 1\n"
+               , UnsafeRaw "declare i32 @printf(ptr noalias nocapture, ...)\n"
+               ]
+
+compileExp :: Exp -> CompilerState ()
+compileExp = \case
+  EInt i        -> emitInt i
+  EAdd t e1 e2  -> emitAdd t e1 e2
+  EId (name, _) -> emitIdent name
+  EApp t e1 e2  -> emitApp t e1 e2
+  EAbs t ti e   -> emitAbs t ti e
+  ELet bind e   -> emitLet bind e
+
+--- aux functions ---
+emitAbs :: Type -> Id -> Exp -> CompilerState ()
+emitAbs _t tid e = emit . Comment $ "Lambda escaped previous stages: \\" <> show tid <> " . " <> show e
+
+emitLet :: Bind -> Exp -> CompilerState ()
+emitLet b e = emit . Comment $ concat [ "ELet ("
+                                      , show b
+                                      , " = "
+                                      , show e
+                                      , ") is not implemented!"
+                                      ]
+
+emitApp :: Type -> Exp -> Exp -> CompilerState ()
+emitApp t e1 e2 = appEmitter t e1 e2 []
+  where
+    appEmitter :: Type -> Exp -> Exp -> [Exp] -> CompilerState ()
+    appEmitter t e1 e2 stack = do
+        let newStack = e2 : stack
+        case e1 of
+            EApp _ e1' e2' -> appEmitter t e1' e2' newStack
+            EId id@(name, _) -> do
+                args <- traverse exprToValue newStack
+                vs <- getNewVar
+                funcs <- gets functions
+                let visibility = maybe Local (const Global) $ Map.lookup id funcs
+                    args'      = map (first valueGetType . dupe) args
+                    call       = Call (type2LlvmType t) visibility name args'
+                emit $ SetVariable (Ident $ show vs) call
+            x -> do
+                emit . Comment $ "The unspeakable happened: "
+                emit . Comment $ show x
+
+emitIdent :: Ident -> CompilerState ()
+emitIdent id = do
+    -- !!this should never happen!!
+    emit $ Comment "This should not have happened!"
+    emit $ Variable id
+    emit $ UnsafeRaw "\n"
+
+emitInt :: Integer -> CompilerState ()
+emitInt i = do
+    -- !!this should never happen!!
+    varCount <- getNewVar
+    emit $ Comment "This should not have happened!"
+    emit $ SetVariable (Ident (show varCount)) (Add I64 (VInteger i) (VInteger 0))
+
+emitAdd :: Type -> Exp -> Exp -> CompilerState ()
+emitAdd t e1 e2 = do
+    v1 <- exprToValue e1
+    v2 <- exprToValue e2
+    v <- getNewVar
+    emit $ SetVariable (Ident $ show v) (Add (type2LlvmType t) v1 v2)
+
+-- emitMul :: Exp -> Exp -> CompilerState ()
+-- emitMul e1 e2 = do
+--     (v1,v2) <- binExprToValues e1 e2
+--     increaseVarCount
+--     v <- gets variableCount
+--     emit $ SetVariable $ Ident $ show v
+--     emit $ Mul I64 v1 v2
+
+-- emitMod :: Exp -> Exp -> CompilerState ()
+-- emitMod e1 e2 = do
+--     -- `let m a b = rem (abs $ b + a) b`
+--     (v1,v2) <- binExprToValues e1 e2
+--     increaseVarCount
+--     vadd <- gets variableCount
+--     emit $ SetVariable $ Ident $ show vadd
+--     emit $ Add I64 v1 v2
+--
+--     increaseVarCount
+--     vabs <- gets variableCount
+--     emit $ SetVariable $ Ident $ show vabs
+--     emit $ Call I64 (Ident "llvm.abs.i64")
+--         [ (I64, VIdent (Ident $ show vadd))
+--         , (I1, VInteger 1)
+--         ]
+--     increaseVarCount
+--     v <- gets variableCount
+--     emit $ SetVariable $ Ident $ show v
+--     emit $ Srem I64 (VIdent (Ident $ show vabs)) v2
+
+-- emitDiv :: Exp -> Exp -> CompilerState ()
+-- emitDiv e1 e2 = do
+--     (v1,v2) <- binExprToValues e1 e2
+--     increaseVarCount
+--     v <- gets variableCount
+--     emit $ SetVariable $ Ident $ show v
+--     emit $ Div I64 v1 v2
+
+-- emitSub :: Exp -> Exp -> CompilerState ()
+-- emitSub e1 e2 = do
+--     (v1,v2) <- binExprToValues e1 e2
+--     increaseVarCount
+--     v <- gets variableCount
+--     emit $ SetVariable $ Ident $ show v
+--     emit $ Sub I64 v1 v2
+
+exprToValue :: Exp -> CompilerState LLVMValue
+exprToValue = \case
+    EInt i -> pure $ VInteger i
+
+    EId id@(name, t) -> do
+        funcs <- gets functions
+        case Map.lookup id funcs of
+            Just fi -> do
+                if numArgs fi == 0
+                    then do
+                        vc <- getNewVar
+                        emit $ SetVariable (Ident $ show vc)
+                            (Call (type2LlvmType t) Global name [])
+                        pure $ VIdent (Ident $ show vc) (type2LlvmType t)
+                    else pure $ VFunction name Global (type2LlvmType t)
+            Nothing -> pure $ VIdent name (type2LlvmType t)
+
+    e -> do
+        compileExp e
+        v <- getVarCount
+        pure $ VIdent (Ident $ show v) (getType e)
+
+type2LlvmType :: Type -> LLVMType
+type2LlvmType = \case
+    TInt -> I64
+    TFun t xs -> do
+        let (t', xs') = function2LLVMType xs [type2LlvmType t]
+        Function t' xs'
+    t -> CustomType $ Ident ("\"" ++ show t ++ "\"")
+  where
+    function2LLVMType :: Type -> [LLVMType] -> (LLVMType, [LLVMType])
+    function2LLVMType (TFun t xs) s = function2LLVMType xs (type2LlvmType t : s)
+    function2LLVMType x s           = (type2LlvmType x, s)
+
+getType :: Exp -> LLVMType
+getType (EInt _)     = I64
+getType (EAdd t _ _) = type2LlvmType t
+getType (EId (_, t)) = type2LlvmType t
+getType (EApp t _ _) = type2LlvmType t
+getType (EAbs t _ _) = type2LlvmType t
+getType (ELet _ e)   = getType e
+
+valueGetType :: LLVMValue -> LLVMType
+valueGetType (VInteger _)      = I64
+valueGetType (VIdent _ t)      = t
+valueGetType (VConstant s)     = Array (length s) I8
+valueGetType (VFunction _ _ t) = t
diff --git a/src/GC/Makefile b/src/GC/Makefile
index 354adad..92b02e8 100644
--- a/src/GC/Makefile
+++ b/src/GC/Makefile
@@ -9,8 +9,8 @@ STDFLAGS 	= -std=gnu++20 -stdlib=libc++
 WFLAGS 		= -Wall -Wextra
 DBGFLAGS 	= -g
 
-test_test:
-	echo "$(shell pwd)"
+advance:
+	$(CC) $(WFLAGS) $(STDFLAGS) tests/advance.cpp -o tests/advance.out
 
 heap:
 	$(CC) $(WFLAGS) $(STDFLAGS) $(LIB_INCL) lib/heap.cpp
diff --git a/src/GC/include/heap.hpp b/src/GC/include/heap.hpp
index 30f1a7a..c70ee54 100644
--- a/src/GC/include/heap.hpp
+++ b/src/GC/include/heap.hpp
@@ -2,9 +2,9 @@
 
 #include <assert.h>
 #include <iostream>
+#include <list>
 #include <setjmp.h>
 #include <stdlib.h>
-#include <vector>
 
 #include "chunk.hpp"
 
@@ -30,26 +30,10 @@ namespace GC {
       m_allocated_size = 0;
     }
 
-    void collect(Heap *heap);
-    void sweep(Heap *heap);
-    uintptr_t *try_recycle_chunks(Heap *heap, size_t size);
-    void free(Heap *heap);
-    void free_overlap(Heap *heap);
-    void mark(uintptr_t *start, const uintptr_t *end, std::vector<Chunk *> worklist);
-    void print_line(Chunk *chunk);
-    void print_worklist(std::vector<Chunk *> list);
-
-    inline static Heap *m_instance = nullptr;
-    const char *m_heap;
-    size_t m_size;
-    size_t m_allocated_size;
-    uintptr_t *m_stack_end = nullptr;
-
-    // maybe change to std::list
-    std::vector<Chunk *> m_allocated_chunks;
-    std::vector<Chunk *> m_freed_chunks;
-
-  public:
+    // BEWARE only for testing, this should be adressed
+    ~Heap() {
+      std::free((char *)m_heap);
+    }
 
     static inline Heap *the() { // TODO: make private
       if (m_instance) // if m_instance is not a nullptr
@@ -58,11 +42,35 @@ namespace GC {
       return m_instance;
     }
 
-    // BEWARE only for testing, this should be adressed
-    ~Heap() {
-      std::free((char *)m_heap);
+    static inline Chunk *getAt(std::list<Chunk *> list, size_t n) {
+      auto iter = list.begin();
+      if (!n)
+        return *iter;
+      std::advance(iter, n);
+      return *iter;
     }
 
+    void collect();
+    void sweep(Heap *heap);
+    uintptr_t *try_recycle_chunks(size_t size);
+    void free(Heap* heap);
+    void free_overlap(Heap *heap);
+    void mark(uintptr_t *start, const uintptr_t *end, std::list<Chunk *> worklist);
+    void print_line(Chunk *chunk);
+    void print_worklist(std::list<Chunk *> list);
+
+    inline static Heap *m_instance = nullptr;
+    const char *m_heap;
+    size_t m_size;
+    size_t m_allocated_size;
+    uintptr_t *m_stack_top = nullptr;
+
+    // maybe change to std::list
+    std::list<Chunk *> m_allocated_chunks;
+    std::list<Chunk *> m_freed_chunks;
+
+  public:
+
     /**
      * These are the only two functions which are exposed
      * as the API for LLVM. At the absolute start of the
@@ -70,8 +78,9 @@ namespace GC {
      * that the address of the topmost stack frame is
      * saved as the limit for scanning the stack in collect.
     */
-    void *alloc(size_t size); // TODO: make static
-    void init(); // TODO: make static
+    static void init();              // TODO: make static
+    static void dispose();           // -||-
+    static void *alloc(size_t size); // -||-
     
     // DEBUG ONLY
     void collect(uint flags); // conditional collection
diff --git a/src/GC/lib/heap.cpp b/src/GC/lib/heap.cpp
index 3d37a3c..c17f680 100644
--- a/src/GC/lib/heap.cpp
+++ b/src/GC/lib/heap.cpp
@@ -14,13 +14,21 @@ namespace GC {
 
   /**
    * Initialises the heap singleton and saves the address
-   * of the calling stack frame as the stack_end. Presumeably
+   * of the calling stack frame as the stack_top. Presumeably
    * this address points to the stack frame of the compiled
    * LLVM executable after linking.
   */
   void Heap::init() {
     Heap *heap = Heap::the();
-    heap->m_stack_end = reinterpret_cast<uintptr_t *>(__builtin_frame_address(1));
+    heap->m_stack_top = reinterpret_cast<uintptr_t *>(__builtin_frame_address(1));
+  }
+
+  /**
+   * Disposes the heap at program exit.
+  */
+  void Heap::dispose() {
+    Heap *heap = Heap::the();
+    delete heap;
   }
 
   /**
@@ -43,13 +51,13 @@ namespace GC {
     }
 
     if (heap->m_size + size > HEAP_SIZE) {
-      collect(heap);
+      heap->collect();
       // If collect failed, crash with OOM error
       assert(heap->m_size + size <= HEAP_SIZE && "Heap: Out Of Memory");
     }
 
     // If a chunk was recycled, return the old chunk address
-    uintptr_t *reused_chunk = try_recycle_chunks(heap, size);
+    uintptr_t *reused_chunk = heap->try_recycle_chunks(size);
     if (reused_chunk != nullptr) {
       return (void *)reused_chunk;
     }
@@ -58,7 +66,7 @@ namespace GC {
     // then create a new chunk
     auto new_chunk = new Chunk;
     new_chunk->size = size;
-    new_chunk->start = (uintptr_t *)(heap->m_heap + m_size);
+    new_chunk->start = (uintptr_t *)(heap->m_heap + heap->m_size);
 
     heap->m_size += size;
 
@@ -75,8 +83,6 @@ namespace GC {
    * objects slightly which saves time from malloc'ing
    * memory from the OS.
    * 
-   * @param heap Pointer to the singleton Heap instance
-   * 
    * @param size  Amount of bytes needed for the object
    *              which is about to be allocated.
    * 
@@ -86,10 +92,14 @@ namespace GC {
    *          nullptr is returned to signify no
    *          chunks were found.
   */
-  uintptr_t *Heap::try_recycle_chunks(Heap *heap, size_t size) {
+  uintptr_t *Heap::try_recycle_chunks(size_t size) {
+    auto heap = Heap::the();
     // Check if there are any freed chunks large enough for current request
     for (size_t i = 0; i < heap->m_freed_chunks.size(); i++) {
-      auto cp = heap->m_freed_chunks.at(i);
+      // auto cp = heap->m_freed_chunks.at(i);
+      auto cp = getAt(heap->m_freed_chunks, i);
+      auto iter = heap->m_freed_chunks.begin();
+      advance(iter, i);
       if (cp->size > size)
       {
         // Split the chunk, use one part and add the remaining part to
@@ -100,7 +110,7 @@ namespace GC {
         chunk_complement->size = diff;
         chunk_complement->start = cp->start + cp->size;
 
-        heap->m_freed_chunks.erase(m_freed_chunks.begin() + i);
+        heap->m_freed_chunks.erase(iter);
         heap->m_freed_chunks.push_back(chunk_complement);
         heap->m_allocated_chunks.push_back(cp);
         
@@ -109,7 +119,7 @@ namespace GC {
       else if (cp->size == size)
       {
         // Reuse the whole chunk
-        heap->m_freed_chunks.erase(m_freed_chunks.begin() + i);
+        heap->m_freed_chunks.erase(iter);
         heap->m_allocated_chunks.push_back(cp);
         return cp->start;
       }
@@ -123,24 +133,23 @@ namespace GC {
    * left on the heap, a collection is triggered. This
    * function is private so that the user cannot trigger
    * a collection unneccessarily.
-   * 
-   * @param heap  Heap singleton instance, only for avoiding
-   *              redundant calls to the singleton get
   */
-  void Heap::collect(Heap *heap) {
+  void Heap::collect() {
+    // Get instance 
+    auto heap = Heap::the();
 
     // get current stack
-    auto stack_start = reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
+    auto stack_bottom = reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
 
     // fix this block, it's nästy
-    uintptr_t *stack_end;
-    if (heap->m_stack_end != nullptr)
-      stack_end = heap->m_stack_end;
+    uintptr_t *stack_top;
+    if (heap->m_stack_top != nullptr)
+      stack_top = heap->m_stack_top;
     else
-      stack_end = (uintptr_t *)0; // temporary
+      stack_top = (uintptr_t *)0; // temporary
 
     auto work_list = heap->m_allocated_chunks;
-    mark(stack_start, stack_end, work_list);
+    mark(stack_bottom, stack_top, work_list);
 
     sweep(heap);
 
@@ -148,24 +157,26 @@ namespace GC {
   }
 
   /**
-    * Iterates through the stack, if an element on the stack points to a chunk
-    * that chunk is marked (i.e. reachable). It only marks element which are directly
-    * reachable from the chunk, so no chain of pointers from the stack are detected. 
+    * Iterates through the stack, if an element on the stack points to a chunk, 
+    * called a root chunk, that chunk is marked (i.e. reachable). 
+    * Then it recursively follows all chunks which are possibly reachable from 
+    * the root chunk and mark those chunks. 
     * If a chunk is marked it is removed from the worklist, since it's no longer of
     * concern for this method. 
     * 
     * @param start    Pointer to the start of the stack frame.
     * @param end      Pointer to the end of the stack frame.
-    * @param worklist The currently allocated chunks. 
+    * @param worklist The currently allocated chunks, which haven't been marked. 
   */ 
-  void Heap::mark(uintptr_t *start, const uintptr_t *end, vector<Chunk*> worklist) {
+  void Heap::mark(uintptr_t *start, const uintptr_t *end, list<Chunk*> worklist) {
     int counter = 0;
     // To find adresses thats in the worklist
     for (; start < end; start++) { 
       counter++;
-      // all pointers must be aligned as double words
-
-      for (auto it = worklist.begin(); it != worklist.end();) {
+      auto it = worklist.begin();
+      auto stop = worklist.end();
+      // for (auto it = worklist.begin(); it != worklist.end();) {
+      while (it != stop) {
         Chunk *chunk = *it;
 
         auto c_start = reinterpret_cast<uintptr_t>(chunk->start);
@@ -181,7 +192,9 @@ namespace GC {
         
           if (!chunk->marked) {
             chunk->marked = true;
+            // Remove the marked chunk from the worklist
             it = worklist.erase(it);
+            // Recursively call mark, to see if the reachable chunk further points to another chunk
             mark((uintptr_t*) c_start, (uintptr_t*) c_end, worklist);
           }
           else {
@@ -198,24 +211,27 @@ namespace GC {
   
   /**
    * Sweeps the heap, unmarks the marked chunks for the next cycle,
-   * adds the unmarked nodes to the vector of freed chunks; to be freed.
+   * adds the unmarked nodes to the list of freed chunks; to be freed.
    * 
-   * @param heap Pointer to the heap to oporate on.
+   * @param heap Pointer to the heap singleton instance.
   */
   void Heap::sweep(Heap *heap) {
-    for (auto it = heap->m_allocated_chunks.begin(); it != heap->m_allocated_chunks.end();) {
-      Chunk *chunk = *it;
+    auto iter = heap->m_allocated_chunks.begin();
+    auto stop = heap->m_allocated_chunks.end();
+    // for (auto it = heap->m_allocated_chunks.begin(); it != heap->m_allocated_chunks.end();) {
+    while (iter != stop) {
+      Chunk *chunk = *iter;
 
       // Unmark the marked chunks for the next iteration.
       if (chunk->marked) {
         chunk->marked = false;
-        ++it;
+        ++iter;
       }
       else {
         // Add the unmarked chunks to freed chunks and remove from
         // the list of allocated chunks 
         heap->m_freed_chunks.push_back(chunk);
-        it = heap->m_allocated_chunks.erase(it);
+        iter = heap->m_allocated_chunks.erase(iter);
       }
     }
   }
@@ -257,13 +273,15 @@ namespace GC {
    *       larger chunks.
   */
   void Heap::free_overlap(Heap *heap) {
-    std::vector<Chunk *> filtered;
+    std::list<Chunk *> filtered;
     size_t i = 0;
-    filtered.push_back(heap->m_freed_chunks.at(i++));
+    // filtered.push_back(heap->m_freed_chunks.at(i++));
+    filtered.push_back(getAt(heap->m_freed_chunks, i++));
     cout << filtered.back()->start << endl;
     for (; i < heap->m_freed_chunks.size(); i++) {
       auto prev = filtered.back();
-      auto next = heap->m_freed_chunks.at(i);
+      // auto next = heap->m_freed_chunks.at(i);
+      auto next = getAt(heap->m_freed_chunks, i);
       auto p_start = (uintptr_t)(prev->start);
       auto p_size  = (uintptr_t)(prev->size);
       auto n_start = (uintptr_t)(next->start);
@@ -283,9 +301,9 @@ namespace GC {
   void Heap::check_init() {
     auto heap = Heap::the();
     cout << "Heap addr:\t" << heap << endl;
-    cout << "GC m_stack_end:\t" << heap->m_stack_end << endl;
-    auto stack_start = reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
-    cout << "GC stack_start:\t" << stack_start << endl;
+    cout << "GC m_stack_top:\t" << heap->m_stack_top << endl;
+    auto stack_bottom = reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
+    cout << "GC stack_bottom:\t" << stack_bottom << endl;
   }
   
   /**
@@ -307,20 +325,20 @@ namespace GC {
     auto heap = Heap::the();
 
     // get the frame adress, whwere local variables and saved registers are located
-    auto stack_start = reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
-    cout << "Stack start in collect:\t" << stack_start << endl;
-    uintptr_t *stack_end;
+    auto stack_bottom = reinterpret_cast<uintptr_t *>(__builtin_frame_address(0));
+    cout << "Stack bottom in collect:\t" << stack_bottom << endl;
+    uintptr_t *stack_top;
 
-    if (heap->m_stack_end != nullptr)
-      stack_end = heap->m_stack_end;
+    if (heap->m_stack_top != nullptr)
+      stack_top = heap->m_stack_top;
     else
-      stack_end = (uintptr_t *) stack_start - 80; // dummy value
+      stack_top = (uintptr_t *) stack_bottom + 80; // dummy value
 
-    cout << "Stack end in collect:\t " << stack_end << endl;
+    cout << "Stack end in collect:\t " << stack_top << endl;
     auto work_list = heap->m_allocated_chunks;
 
     if (flags & MARK) {
-      mark(stack_start, stack_end, work_list);
+      mark(stack_bottom, stack_top, work_list);
     }
 
     if (flags & SWEEP) {
@@ -366,7 +384,7 @@ namespace GC {
     cout << "Marked: " << chunk->marked << "\nStart adr: " << chunk->start << "\nSize: " << chunk->size << " B\n" << endl;
   }
 
-  void Heap::print_worklist(std::vector<Chunk *> list) {
+  void Heap::print_worklist(std::list<Chunk *> list) {
     for (auto cp : list) {
       cout << "Chunk at:\t" << cp->start << "\nSize:\t\t" << cp->size << endl;
     }
diff --git a/src/GC/tests/advance.cpp b/src/GC/tests/advance.cpp
new file mode 100644
index 0000000..0a8a177
--- /dev/null
+++ b/src/GC/tests/advance.cpp
@@ -0,0 +1,34 @@
+#include <iostream>
+#include <list>
+#include <stdlib.h>
+
+using namespace std;
+
+int main() {
+    list<char> l;
+    char c = 'a';
+    for (int i = 1; i <= 5; i++) {
+        l.push_back(c++);
+    }
+
+    auto iter = l.begin();
+    auto stop = l.end();
+
+    while (iter != stop) {
+        cout << *iter << " ";
+     
+        iter++;
+    }
+    cout << endl;
+    iter = l.begin();
+    while (*iter != *stop) {
+        cout << *iter << " ";
+        iter++;
+    }
+    cout << endl;
+
+    cout << "rebased" << endl;
+    // cout << "iter: " << *iter << "\nstop: " << *stop << endl;
+
+    return 0;
+}
\ No newline at end of file
diff --git a/src/GC/todo.md b/src/GC/todo.md
index dba3eee..f9492da 100644
--- a/src/GC/todo.md
+++ b/src/GC/todo.md
@@ -1,18 +1,15 @@
 # Garbage collection
 
-
-
 ## Project
 
 Goal for next week (24/2):
-- Debug 
+- Write more complex tests
 
 ## GC TODO:
 - Merge to main branch
-- Switch std::vector to std::list
-- Make alloc and init static, move the() to private
-- stack_end, stack_start -> stack_top, stack_bottom
 - Double check m_heap_size functionality and when a collection is triggered
+- Kolla vektor vs list complexity
 
 ## Tests TODO
+- Write complex datastructures for tests with larger programs
 
diff --git a/src/Interpreter.hs b/src/Interpreter.hs
index bdbd8d2..37d46a7 100644
--- a/src/Interpreter.hs
+++ b/src/Interpreter.hs
@@ -1,45 +1,78 @@
-{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE LambdaCase          #-}
+{-# LANGUAGE OverloadedRecordDot #-}
+{-# LANGUAGE OverloadedStrings   #-}
 module Interpreter where
 
+import           Auxiliary               (maybeToRightM)
 import           Control.Applicative     (Applicative)
 import           Control.Monad.Except    (Except, MonadError (throwError),
                                           liftEither)
+import           Control.Monad.State     (MonadState, StateT, evalStateT)
 import           Data.Either.Combinators (maybeToRight)
 import           Data.Map                (Map)
 import qualified Data.Map                as Map
+import           Data.Maybe              (maybe)
 import           Grammar.Abs
+import           Grammar.ErrM            (Err)
 import           Grammar.Print           (printTree)
 
-interpret :: Program -> Except String Integer
-interpret (Program e) =
-  eval mempty e >>= \case
-    VClosure {} -> throwError "main evaluated to a function"
-    VInt i      -> pure i
+interpret :: Program -> Err Integer
+interpret (Program scs) = do
+  main <- findMain scs
+  eval (initCxt scs) main >>=
+    \case
+      VClosure {} -> throwError "main evaluated to a function"
+      VInt i      -> pure i
 
 
+initCxt :: [Bind] -> Cxt
+initCxt scs =
+  Cxt { env = mempty
+      , sig = foldr insert mempty $ map expandLambdas scs
+      }
+  where insert (Bind name _ rhs) = Map.insert name rhs
+
+expandLambdas :: Bind -> Bind
+expandLambdas (Bind name parms rhs) = Bind name [] $ foldr EAbs rhs parms
+
+findMain :: [Bind] -> Err Exp
+findMain []       = throwError "No main!"
+findMain (sc:scs) = case sc of
+                      Bind "main" _ rhs -> pure rhs
+                      _                 -> findMain scs
+
 data Val = VInt Integer
-         | VClosure Cxt Ident Exp
+         | VClosure Env Ident Exp
+           deriving (Show, Eq)
 
-type Cxt = Map Ident Val
+type Env = Map Ident Val
+type Sig = Map Ident Exp
 
-eval :: Cxt -> Exp -> Except String Val
+data Cxt = Cxt
+  { env :: Map Ident Val
+  , sig :: Map Ident Exp
+  } deriving (Show, Eq)
+
+eval :: Cxt -> Exp -> Err Val
 eval cxt = \case
 
-
   --  ------------ x ∈ γ
   --  γ ⊢ x ⇓ γ(x)
 
-  EId x     ->
-    maybeToRightM
-      ("Unbound variable:" ++ printTree x)
-      $ Map.lookup x cxt
+  EId x     -> do
+    case Map.lookup x cxt.env of
+      Just e -> pure e
+      Nothing ->
+        case Map.lookup x cxt.sig of
+          Just e  -> eval (emptyEnv cxt) e
+          Nothing -> throwError ("Unbound variable: " ++ printTree x)
 
   --  ---------
   --  γ ⊢ i ⇓ i
 
   EInt i    -> pure $ VInt i
 
-  --  γ     ⊢ e  ⇓ let δ in λx → f
+  --  γ     ⊢ e  ⇓ let δ in λx. f
   --  γ     ⊢ e₁ ⇓ v
   --  δ,x=v ⊢ f  ⇓ v₁
   --  ------------------------------
@@ -50,13 +83,15 @@ eval cxt = \case
       VInt _ -> throwError "Not a function"
       VClosure delta x f -> do
         v <- eval cxt e1
-        eval (Map.insert x v delta) f
+        let cxt' = putEnv (Map.insert x v delta) cxt
+        eval cxt' f
+
 
   --
   --  -----------------------------
-  --  γ ⊢ λx → f ⇓ let γ in λx → f
+  --  γ ⊢ λx. f ⇓ let γ in λx. f
 
-  EAbs x e  -> pure $ VClosure cxt x e
+  EAbs par e  -> pure $ VClosure cxt.env par e
 
 
   --  γ ⊢ e  ⇓ v
@@ -71,8 +106,11 @@ eval cxt = \case
       (VInt i, VInt i1) -> pure $ VInt (i + i1)
       _                 -> throwError "Can't add a function"
 
+  ELet _ _ -> throwError "ELet pattern match should never occur!"
 
 
-maybeToRightM :: MonadError l m => l -> Maybe r -> m r
-maybeToRightM err = liftEither . maybeToRight err
+emptyEnv :: Cxt -> Cxt
+emptyEnv cxt = cxt { env = mempty }
 
+putEnv :: Env -> Cxt -> Cxt
+putEnv env cxt = cxt { env = env }
diff --git a/src/LambdaLifter.hs b/src/LambdaLifter.hs
new file mode 100644
index 0000000..015e7f3
--- /dev/null
+++ b/src/LambdaLifter.hs
@@ -0,0 +1,190 @@
+{-# LANGUAGE LambdaCase        #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+
+module LambdaLifter (lambdaLift, freeVars, abstract, rename, collectScs) where
+
+import           Auxiliary           (snoc)
+import           Control.Applicative (Applicative (liftA2))
+import           Control.Monad.State (MonadState (get, put), State, evalState)
+import           Data.Set            (Set)
+import qualified Data.Set            as Set
+import           Prelude             hiding (exp)
+import           Renamer
+import           TypeCheckerIr
+
+
+-- | Lift lambdas and let expression into supercombinators.
+-- Three phases:
+-- @freeVars@ annotatss all the free variables.
+-- @abstract@ converts lambdas into let expressions.
+-- @collectScs@ moves every non-constant let expression to a top-level function.
+lambdaLift :: Program -> Program
+lambdaLift = collectScs . abstract . freeVars
+
+
+-- | Annotate free variables
+freeVars :: Program -> AnnProgram
+freeVars (Program ds) = [ (n, xs, freeVarsExp (Set.fromList xs) e)
+                        | Bind n xs e <- ds
+                        ]
+
+freeVarsExp :: Set Id -> Exp -> AnnExp
+freeVarsExp localVars = \case
+    EId  n  | Set.member n localVars -> (Set.singleton n, AId n)
+            | otherwise              -> (mempty, AId n)
+
+    EInt i -> (mempty, AInt i)
+
+    EApp t e1 e2 -> (Set.union (freeVarsOf e1') (freeVarsOf e2'), AApp t e1' e2')
+      where
+        e1' = freeVarsExp localVars e1
+        e2' = freeVarsExp localVars e2
+
+    EAdd t e1 e2 -> (Set.union (freeVarsOf e1') (freeVarsOf e2'), AAdd t e1' e2')
+      where
+        e1' = freeVarsExp localVars e1
+        e2' = freeVarsExp localVars e2
+
+    EAbs t par e -> (Set.delete par $ freeVarsOf e', AAbs t par e')
+      where
+        e' = freeVarsExp (Set.insert par localVars) e
+
+    -- Sum free variables present in bind and the expression
+    ELet (Bind name parms rhs) e  -> (Set.union binders_frees e_free, ALet new_bind e')
+      where
+        binders_frees = Set.delete name $ freeVarsOf rhs'
+        e_free        = Set.delete name $ freeVarsOf e'
+
+        rhs'     = freeVarsExp e_localVars rhs
+        new_bind = ABind name parms rhs'
+
+        e'          = freeVarsExp e_localVars e
+        e_localVars = Set.insert name localVars
+
+
+freeVarsOf :: AnnExp -> Set Id
+freeVarsOf = fst
+
+-- AST annotated with free variables
+type AnnProgram = [(Id, [Id], AnnExp)]
+
+type AnnExp = (Set Id, AnnExp')
+
+data ABind = ABind Id [Id] AnnExp deriving Show
+
+data AnnExp' = AId  Id
+             | AInt Integer
+             | ALet ABind AnnExp
+             | AApp Type    AnnExp  AnnExp
+             | AAdd Type    AnnExp  AnnExp
+             | AAbs Type    Id      AnnExp
+             deriving Show
+-- | Lift lambdas to let expression of the form @let sc = \v₁ x₁ -> e₁@.
+-- Free variables are @v₁ v₂ .. vₙ@ are bound.
+abstract :: AnnProgram -> Program
+abstract prog = Program $ evalState (mapM go prog) 0
+  where
+    go :: (Id, [Id], AnnExp) -> State Int Bind
+    go (name, parms, rhs) = Bind name (parms ++ parms1) <$> abstractExp rhs'
+      where
+        (rhs', parms1) = flattenLambdasAnn rhs
+
+
+-- | Flatten nested lambdas and collect the parameters
+-- @\x.\y.\z. ae → (ae, [x,y,z])@
+flattenLambdasAnn :: AnnExp -> (AnnExp, [Id])
+flattenLambdasAnn ae = go (ae, [])
+  where
+    go :: (AnnExp, [Id]) -> (AnnExp, [Id])
+    go ((free, e), acc) =
+        case e of
+            AAbs _ par (free1, e1) ->
+                go ((Set.delete par free1, e1), snoc par acc)
+            _ -> ((free, e), acc)
+
+abstractExp :: AnnExp -> State Int Exp
+abstractExp (free, exp) = case exp of
+    AId  n       -> pure $ EId  n
+    AInt i       -> pure $ EInt i
+    AApp t e1 e2 -> liftA2 (EApp t) (abstractExp e1) (abstractExp e2)
+    AAdd t e1 e2 -> liftA2 (EAdd t) (abstractExp e1) (abstractExp e2)
+    ALet b e     -> liftA2 ELet (go b) (abstractExp e)
+      where
+        go (ABind name parms rhs) = do
+            (rhs', parms1)  <- flattenLambdas <$> skipLambdas abstractExp rhs
+            pure $ Bind name (parms ++ parms1) rhs'
+
+        skipLambdas :: (AnnExp -> State Int Exp) -> AnnExp -> State Int Exp
+        skipLambdas f (free, ae) = case ae of
+            AAbs t par ae1 -> EAbs t par <$> skipLambdas f ae1
+            _              -> f (free, ae)
+
+    -- Lift lambda into let and bind free variables
+    AAbs t parm e -> do
+        i <- nextNumber
+        rhs <- abstractExp e
+
+        let sc_name = Ident ("sc_" ++ show i)
+            sc      = ELet (Bind (sc_name, t) parms rhs) $ EId (sc_name, t)
+
+        pure $ foldl (EApp TInt) sc $ map EId freeList
+      where
+        freeList = Set.toList free
+        parms    = snoc parm freeList
+
+
+nextNumber :: State Int Int
+nextNumber = do
+    i <- get
+    put $ succ i
+    pure i
+
+-- | Collects supercombinators by lifting non-constant let expressions
+collectScs :: Program -> Program
+collectScs (Program scs) = Program $ concatMap collectFromRhs scs
+  where
+    collectFromRhs (Bind name parms rhs) =
+        let (rhs_scs, rhs') = collectScsExp rhs
+        in  Bind name parms rhs' : rhs_scs
+
+
+collectScsExp :: Exp -> ([Bind], Exp)
+collectScsExp = \case
+    EId  n -> ([], EId n)
+    EInt i -> ([], EInt i)
+
+    EApp t e1 e2 -> (scs1 ++ scs2, EApp t e1' e2')
+      where
+        (scs1, e1') = collectScsExp e1
+        (scs2, e2') = collectScsExp e2
+
+    EAdd t e1 e2 -> (scs1 ++ scs2, EAdd t e1' e2')
+      where
+        (scs1, e1') = collectScsExp e1
+        (scs2, e2') = collectScsExp e2
+
+    EAbs t par e -> (scs, EAbs t par e')
+      where
+        (scs, e') = collectScsExp e
+
+    -- Collect supercombinators from bind, the rhss, and the expression.
+    --
+    -- > f = let sc x y = rhs in e
+    --
+    ELet (Bind name parms rhs) e -> if null parms
+                                    then (       rhs_scs ++ e_scs, ELet bind e')
+                                    else (bind : rhs_scs ++ e_scs, e')
+      where
+        bind            = Bind name parms rhs'
+        (rhs_scs, rhs') = collectScsExp rhs
+        (e_scs, e')     = collectScsExp e
+
+
+-- @\x.\y.\z. e → (e, [x,y,z])@
+flattenLambdas :: Exp -> (Exp, [Id])
+flattenLambdas = go . (, [])
+  where
+    go (e, acc) = case e of
+                      EAbs _ par e1 -> go (e1, snoc par acc)
+                      _             -> (e, acc)
diff --git a/src/LlvmIr.hs b/src/LlvmIr.hs
new file mode 100644
index 0000000..d340ddc
--- /dev/null
+++ b/src/LlvmIr.hs
@@ -0,0 +1,204 @@
+{-# LANGUAGE LambdaCase #-}
+
+module LlvmIr (
+    LLVMType (..),
+    LLVMIr (..),
+    llvmIrToString,
+    LLVMValue (..),
+    LLVMComp (..),
+    Visibility (..),
+) where
+
+import           Data.List     (intercalate)
+import           TypeCheckerIr
+
+-- | A datatype which represents some basic LLVM types
+data LLVMType
+    = I1
+    | I8
+    | I32
+    | I64
+    | Ptr
+    | Ref LLVMType
+    | Function LLVMType [LLVMType]
+    | Array Int LLVMType
+    | CustomType Ident
+
+instance Show LLVMType where
+    show :: LLVMType -> String
+    show = \case
+        I1 -> "i1"
+        I8 -> "i8"
+        I32 -> "i32"
+        I64 -> "i64"
+        Ptr -> "ptr"
+        Ref ty -> show ty <> "*"
+        Function t xs -> show t <> " (" <> intercalate ", " (map show xs) <> ")*"
+        Array n ty -> concat ["[", show n, " x ", show ty, "]"]
+        CustomType (Ident ty) -> ty
+
+data LLVMComp
+    = LLEq
+    | LLNe
+    | LLUgt
+    | LLUge
+    | LLUlt
+    | LLUle
+    | LLSgt
+    | LLSge
+    | LLSlt
+    | LLSle
+instance Show LLVMComp where
+    show :: LLVMComp -> String
+    show = \case
+        LLEq  -> "eq"
+        LLNe  -> "ne"
+        LLUgt -> "ugt"
+        LLUge -> "uge"
+        LLUlt -> "ult"
+        LLUle -> "ule"
+        LLSgt -> "sgt"
+        LLSge -> "sge"
+        LLSlt -> "slt"
+        LLSle -> "sle"
+
+data Visibility = Local | Global
+instance Show Visibility where
+    show :: Visibility -> String
+    show Local  = "%"
+    show Global = "@"
+
+-- | Represents a LLVM "value", as in an integer, a register variable,
+-- or a string contstant
+data LLVMValue
+    = VInteger Integer
+    | VIdent Ident LLVMType
+    | VConstant String
+    | VFunction Ident Visibility LLVMType
+
+instance Show LLVMValue where
+    show :: LLVMValue -> String
+    show v = case v of
+        VInteger i                -> show i
+        VIdent (Ident n) _        -> "%" <> n
+        VFunction (Ident n) vis _ -> show vis <> n
+        VConstant s               -> "c" <> show s
+
+type Params = [(Ident, LLVMType)]
+type Args = [(LLVMType, LLVMValue)]
+
+-- | A datatype which represents different instructions in LLVM
+data LLVMIr
+    = Define LLVMType Ident Params
+    | DefineEnd
+    | Declare LLVMType Ident Params
+    | SetVariable Ident LLVMIr
+    | Variable Ident
+    | Add LLVMType LLVMValue LLVMValue
+    | Sub LLVMType LLVMValue LLVMValue
+    | Div LLVMType LLVMValue LLVMValue
+    | Mul LLVMType LLVMValue LLVMValue
+    | Srem LLVMType LLVMValue LLVMValue
+    | Icmp LLVMComp LLVMType LLVMValue LLVMValue
+    | Br Ident
+    | BrCond LLVMValue Ident Ident
+    | Label Ident
+    | Call LLVMType Visibility Ident Args
+    | Alloca LLVMType
+    | Store LLVMType Ident LLVMType Ident
+    | Bitcast LLVMType Ident LLVMType
+    | Ret LLVMType LLVMValue
+    | Comment String
+    | UnsafeRaw String -- This should generally be avoided, and proper
+    -- instructions should be used in its place
+    deriving (Show)
+
+-- | Converts a list of LLVMIr instructions to a string
+llvmIrToString :: [LLVMIr] -> String
+llvmIrToString = go 0
+  where
+    go :: Int -> [LLVMIr] -> String
+    go _ [] = mempty
+    go i (x : xs) = do
+        let (i', n) = case x of
+                Define{}  -> (i + 1, 0)
+                DefineEnd -> (i - 1, 0)
+                _         -> (i, i)
+        insToString n x <> go i' xs
+
+-- | Converts a LLVM inststruction to a String, allowing for printing etc.
+-- The integer represents the indentation
+insToString :: Int -> LLVMIr -> String
+insToString i l =
+    replicate i '\t' <> case l of
+        (Define t (Ident i) params) ->
+            concat
+                [ "define ", show t, " @", i
+                , "(", intercalate ", " (map (\(Ident y, x) -> unwords [show x, "%" <> y]) params)
+                , ") {\n"
+                ]
+        DefineEnd -> "}\n"
+        (Declare _t (Ident _i) _params) -> undefined
+        (SetVariable (Ident i) ir) -> concat ["%", i, " = ", insToString 0 ir]
+        (Add t v1 v2) ->
+            concat
+                [ "add ", show t, " ", show v1
+                , ", ", show v2, "\n"
+                ]
+        (Sub t v1 v2) ->
+            concat
+                [ "sub ", show t, " ", show v1, ", "
+                , show v2, "\n"
+                ]
+        (Div t v1 v2) ->
+            concat
+                [ "sdiv ", show t, " ", show v1, ", "
+                , show v2, "\n"
+                ]
+        (Mul t v1 v2) ->
+            concat
+                [ "mul ", show t, " ", show v1
+                , ", ", show v2, "\n"
+                ]
+        (Srem t v1 v2) ->
+            concat
+                [ "srem ", show t, " ", show v1, ", "
+                , show v2, "\n"
+                ]
+        (Call t vis (Ident i) arg) ->
+            concat
+                [ "call ", show t, " ", show vis, i, "("
+                , intercalate ", " $ Prelude.map (\(x, y) -> show x <> " " <> show y) arg
+                , ")\n"
+                ]
+        (Alloca t) -> unwords ["alloca", show t, "\n"]
+        (Store t1 (Ident id1) t2 (Ident id2)) ->
+            concat
+                [ "store ", show t1, " %", id1
+                , ", ", show t2 , " %", id2, "\n"
+                ]
+        (Bitcast t1 (Ident i) t2) ->
+            concat
+                [ "bitcast ", show t1, " %"
+                , i, " to ", show t2, "\n"
+                ]
+        (Icmp comp t v1 v2) ->
+            concat
+                [ "icmp ", show comp, " ", show t
+                , " ", show v1, ", ", show v2, "\n"
+                ]
+        (Ret t v) ->
+            concat
+                [ "ret ", show t, " "
+                , show v, "\n"
+                ]
+        (UnsafeRaw s) -> s
+        (Label (Ident s)) -> "\nlabel_" <> s <> ":\n"
+        (Br (Ident s)) -> "br label %label_" <> s <> "\n"
+        (BrCond val (Ident s1) (Ident s2)) ->
+            concat
+                [ "br i1 ", show val, ", ", "label %"
+                , "label_", s1, ", ", "label %", "label_", s2, "\n"
+                ]
+        (Comment s) -> "; " <> s <> "\n"
+        (Variable (Ident id)) -> "%" <> id
diff --git a/src/Main.hs b/src/Main.hs
index ed753f2..1831428 100644
--- a/src/Main.hs
+++ b/src/Main.hs
@@ -1,30 +1,97 @@
 {-# LANGUAGE LambdaCase #-}
+
 module Main where
 
-import           Control.Monad.Except (runExcept)
-import           Grammar.Par          (myLexer, pProgram)
-import           Interpreter          (interpret)
-import           System.Environment   (getArgs)
-import           System.Exit          (exitFailure, exitSuccess)
+import Compiler (compile)
+import GHC.IO.Handle.Text (hPutStrLn)
+import Grammar.ErrM (Err)
+import Grammar.Par (myLexer, pProgram)
+import Grammar.Print (printTree)
+
+-- import           Interpreter        (interpret)
+import LambdaLifter (lambdaLift)
+import Renamer (rename)
+import System.Environment (getArgs)
+import System.Exit (exitFailure, exitSuccess)
+import System.IO (stderr)
+import TypeChecker (typecheck)
 
 main :: IO ()
-main = getArgs >>= \case
-  []    -> print "Required file path missing"
-  (x:_) -> do
-    file <- readFile x
-    case pProgram (myLexer file) of
-      Left err -> do
-       putStrLn "SYNTAX ERROR"
-       putStrLn err
-       exitFailure
-      Right prg -> case runExcept $ interpret prg of
-        Left err -> do
-          putStrLn "INTERPRETER ERROR"
-          putStrLn err
-          exitFailure
-        Right i -> do
-          print i
-          exitSuccess
+main =
+    getArgs >>= \case
+        [] -> print "Required file path missing"
+        (s : _) -> main' s
 
+main' :: String -> IO ()
+main' s = do
+    file <- readFile s
 
+    printToErr "-- Parse Tree -- "
+    parsed <- fromSyntaxErr . pProgram $ myLexer file
+    printToErr $ printTree parsed
 
+    printToErr "\n-- Renamer --"
+    let renamed = rename parsed
+    printToErr $ printTree renamed
+
+    printToErr "\n-- TypeChecker --"
+    typechecked <- fromTypeCheckerErr $ typecheck renamed
+    printToErr $ printTree typechecked
+
+    printToErr "\n-- Lambda Lifter --"
+    let lifted = lambdaLift typechecked
+    printToErr $ printTree lifted
+
+    printToErr "\n -- Printing compiler output to stdout --"
+    compiled <- fromCompilerErr $ compile lifted
+    putStrLn compiled
+    writeFile "llvm.ll" compiled
+
+    -- interpred <- fromInterpreterErr $ interpret lifted
+    -- putStrLn "\n-- interpret"
+    -- print interpred
+
+    exitSuccess
+
+printToErr :: String -> IO ()
+printToErr = hPutStrLn stderr
+
+fromCompilerErr :: Err a -> IO a
+fromCompilerErr =
+    either
+        ( \err -> do
+            putStrLn "\nCOMPILER ERROR"
+            putStrLn err
+            exitFailure
+        )
+        pure
+
+fromSyntaxErr :: Err a -> IO a
+fromSyntaxErr =
+    either
+        ( \err -> do
+            putStrLn "\nSYNTAX ERROR"
+            putStrLn err
+            exitFailure
+        )
+        pure
+
+fromTypeCheckerErr :: Err a -> IO a
+fromTypeCheckerErr =
+    either
+        ( \err -> do
+            putStrLn "\nTYPECHECKER ERROR"
+            putStrLn err
+            exitFailure
+        )
+        pure
+
+fromInterpreterErr :: Err a -> IO a
+fromInterpreterErr =
+    either
+        ( \err -> do
+            putStrLn "\nINTERPRETER ERROR"
+            putStrLn err
+            exitFailure
+        )
+        pure
diff --git a/src/Renamer.hs b/src/Renamer.hs
new file mode 100644
index 0000000..b284e92
--- /dev/null
+++ b/src/Renamer.hs
@@ -0,0 +1,84 @@
+{-# LANGUAGE LambdaCase #-}
+
+module Renamer (module Renamer) where
+
+import           Auxiliary           (mapAccumM)
+import           Control.Monad.State (MonadState, State, evalState, gets,
+                                      modify)
+import           Data.Map            (Map)
+import qualified Data.Map            as Map
+import           Data.Maybe          (fromMaybe)
+import           Data.Tuple.Extra    (dupe)
+import           Grammar.Abs
+
+
+-- | Rename all variables and local binds
+rename :: Program -> Program
+rename (Program bs) = Program $ evalState (runRn $ mapM (renameSc initNames) bs) 0
+  where
+    initNames = Map.fromList $ map (\(Bind name _ _ _ _) -> dupe name) bs
+    renameSc :: Names -> Bind -> Rn Bind
+    renameSc old_names (Bind name t _ parms rhs) = do
+        (new_names, parms') <- newNames old_names parms
+        rhs'                <- snd <$> renameExp new_names rhs
+        pure $ Bind name t name parms' rhs'
+
+
+-- | Rename monad. State holds the number of renamed names.
+newtype Rn a = Rn { runRn :: State Int a }
+  deriving (Functor, Applicative, Monad, MonadState Int)
+
+-- | Maps old to new name
+type Names = Map Ident Ident
+
+renameLocalBind :: Names -> Bind -> Rn (Names, Bind)
+renameLocalBind old_names (Bind name t _ parms rhs) = do
+    (new_names, name')   <- newName old_names name
+    (new_names', parms') <- newNames new_names parms
+    (new_names'', rhs')  <- renameExp new_names' rhs
+    pure (new_names'', Bind name' t name' parms' rhs')
+
+renameExp :: Names -> Exp -> Rn (Names, Exp)
+renameExp old_names = \case
+    EId  n     -> pure (old_names, EId . fromMaybe n $ Map.lookup n old_names)
+
+    EInt i1    -> pure (old_names, EInt i1)
+
+    EApp e1 e2 -> do
+        (env1, e1') <- renameExp old_names e1
+        (env2, e2') <- renameExp old_names e2
+        pure (Map.union env1 env2, EApp e1' e2')
+
+    EAdd e1 e2 -> do
+        (env1, e1') <- renameExp old_names e1
+        (env2, e2') <- renameExp old_names e2
+        pure (Map.union env1 env2, EAdd e1' e2')
+
+    ELet b e  -> do
+        (new_names, b)   <- renameLocalBind old_names b
+        (new_names', e') <- renameExp new_names e
+        pure (new_names', ELet b e')
+
+    EAbs par t e  -> do
+        (new_names, par') <- newName old_names par
+        (new_names', e')  <- renameExp new_names e
+        pure (new_names', EAbs par' t e')
+
+    EAnn e t -> do
+        (new_names, e') <- renameExp old_names e
+        pure (new_names, EAnn e' t)
+
+-- | Create a new name and add it to name environment.
+newName :: Names -> Ident -> Rn (Names, Ident)
+newName env old_name = do
+    new_name <- makeName old_name
+    pure (Map.insert old_name new_name env, new_name)
+
+-- | Create multiple names and add them to the name environment
+newNames :: Names -> [Ident] -> Rn (Names, [Ident])
+newNames = mapAccumM newName
+
+-- | Annotate name with number and increment the number @prefix ⇒ prefix_number@.
+makeName :: Ident -> Rn Ident
+makeName (Ident prefix) = gets (\i -> Ident $ prefix ++ "_" ++ show i) <* modify succ
+
diff --git a/src/TypeChecker.hs b/src/TypeChecker.hs
index e69de29..1e44888 100644
--- a/src/TypeChecker.hs
+++ b/src/TypeChecker.hs
@@ -0,0 +1,178 @@
+{-# LANGUAGE LambdaCase          #-}
+{-# LANGUAGE OverloadedRecordDot #-}
+
+module TypeChecker (typecheck, partitionType) where
+
+import           Auxiliary            (maybeToRightM, snoc)
+import           Control.Monad.Except (throwError, unless)
+import           Data.Map             (Map)
+import qualified Data.Map             as Map
+import           Grammar.Abs
+import           Grammar.ErrM         (Err)
+import           Grammar.Print        (Print (prt), concatD, doc, printTree,
+                                       render)
+import           Prelude              hiding (exp, id)
+import qualified TypeCheckerIr        as T
+
+-- NOTE: this type checker is poorly tested
+
+-- TODO
+-- Coercion
+-- Type inference
+
+data Cxt = Cxt
+    { env :: Map Ident Type -- ^ Local scope signature
+    , sig :: Map Ident Type -- ^ Top-level signatures
+    }
+
+initCxt :: [Bind] -> Cxt
+initCxt sc = Cxt { env = mempty
+                 , sig = Map.fromList $ map (\(Bind n t _ _ _) -> (n, t)) sc
+                 }
+
+typecheck :: Program -> Err T.Program
+typecheck (Program sc) = T.Program <$> mapM (checkBind $ initCxt sc) sc
+
+-- | Check if infered rhs type matches type signature.
+checkBind :: Cxt -> Bind -> Err T.Bind
+checkBind cxt b =
+    case expandLambdas b of
+        Bind name t _ parms rhs -> do
+            (rhs', t_rhs) <- infer cxt rhs
+            unless (typeEq t_rhs t) . throwError $ typeErr name t t_rhs
+            pure $ T.Bind (name, t) (zip parms ts_parms) rhs'
+          where
+            ts_parms = fst $ partitionType (length parms) t
+
+-- | @ f x y = rhs ⇒ f = \x.\y. rhs @
+expandLambdas :: Bind -> Bind
+expandLambdas (Bind name t _ parms rhs) = Bind name t name [] rhs'
+  where
+    rhs'     = foldr ($) rhs $ zipWith EAbs parms ts_parms
+    ts_parms = fst $ partitionType (length parms) t
+
+-- | Infer type of expression.
+infer :: Cxt -> Exp -> Err (T.Exp, Type)
+infer cxt = \case
+    EId x ->
+        case lookupEnv x cxt of
+            Nothing ->
+                case lookupSig x cxt of
+                    Nothing -> throwError ("Unbound variable:" ++ printTree x)
+                    Just t  -> pure (T.EId (x, t), t)
+            Just t -> pure (T.EId (x, t), t)
+
+    EInt i -> pure (T.EInt i, T.TInt)
+
+    EApp e e1 -> do
+        (e', t) <- infer cxt e
+        case t of
+            TFun t1 t2 -> do
+                e1' <- check cxt e1 t1
+                pure (T.EApp t2 e' e1', t2)
+            _ -> do
+                throwError ("Not a function: " ++ show e)
+
+    EAdd e e1 -> do
+        e'  <- check cxt e T.TInt
+        e1' <- check cxt e1 T.TInt
+        pure (T.EAdd T.TInt e' e1', T.TInt)
+
+    EAbs x t e  -> do
+        (e', t1) <- infer (insertEnv x t cxt) e
+        let t_abs = TFun t t1
+        pure (T.EAbs t_abs (x, t) e', t_abs)
+
+    ELet b e -> do
+        let cxt' = insertBind b cxt
+        b'    <- checkBind cxt' b
+        (e', t) <- infer cxt' e
+        pure (T.ELet b' e', t)
+
+    EAnn e t -> do
+        (e', t1) <- infer cxt e
+        unless (typeEq t t1) $
+            throwError "Inferred type and type annotation doesn't match"
+        pure (e', t1)
+
+-- | Check infered type matches the supplied type.
+check :: Cxt -> Exp -> Type -> Err T.Exp
+check cxt exp typ = case exp of
+
+    EId x     -> do
+        t <- case lookupEnv x cxt of
+            Nothing -> maybeToRightM
+                           ("Unbound variable:" ++ printTree x)
+                           (lookupSig x cxt)
+            Just t -> pure t
+        unless (typeEq t typ) . throwError $ typeErr x typ t
+        pure $ T.EId (x, t)
+
+    EInt i    -> do
+        unless (typeEq typ TInt) $ throwError $ typeErr i TInt typ
+        pure $ T.EInt i
+
+    EApp e e1 -> do
+        (e', t) <- infer cxt e
+        case t of
+            TFun t1 t2 -> do
+              e1' <- check cxt e1 t1
+              pure $ T.EApp t2 e' e1'
+            _    -> throwError ("Not a function 2: " ++ printTree e)
+
+    EAdd e e1 -> do
+        e'  <- check cxt e T.TInt
+        e1' <- check cxt e1 T.TInt
+        pure $ T.EAdd T.TInt e' e1'
+
+    EAbs x t e  -> do
+        (e', t_e) <- infer (insertEnv x t cxt) e
+        let t1 = TFun t t_e
+        unless (typeEq t1 typ) $ throwError "Wrong lamda type!"
+        pure $ T.EAbs t1 (x, t) e'
+
+    ELet b e -> do
+        let cxt' = insertBind b cxt
+        b' <- checkBind cxt' b
+        e' <- check cxt' e typ
+        pure $ T.ELet b' e'
+
+    EAnn e t -> do
+        unless (typeEq t typ) $
+            throwError "Inferred type and type annotation doesn't match"
+        check cxt e t
+
+-- | Check if types are equivalent. Doesn't handle coercion or polymorphism.
+typeEq :: Type -> Type -> Bool
+typeEq (TFun t t1) (TFun q q1) = typeEq t q && typeEq t1 q1
+typeEq t           t1          = t == t1
+
+-- | Partion type into types of parameters and return type.
+partitionType :: Int -- Number of parameters to apply
+              -> Type
+              -> ([Type], Type)
+partitionType = go []
+  where
+    go acc 0 t = (acc, t)
+    go acc i t = case t of
+        TFun t1 t2 -> go (snoc t1 acc) (i - 1) t2
+        _          -> error "Number of parameters and type doesn't match"
+
+insertBind :: Bind -> Cxt -> Cxt
+insertBind (Bind n t _ _ _) = insertEnv n t
+
+lookupEnv :: Ident -> Cxt -> Maybe Type
+lookupEnv x = Map.lookup x . env
+
+insertEnv :: Ident -> Type -> Cxt -> Cxt
+insertEnv x t cxt = cxt { env = Map.insert x t cxt.env }
+
+lookupSig :: Ident -> Cxt -> Maybe Type
+lookupSig x = Map.lookup x . sig
+
+typeErr :: Print a => a -> Type -> Type -> String
+typeErr p expected actual =  render $ concatD
+    [ doc $ showString "Wrong type:", prt 0 p       , doc $ showString "\n"
+    , doc $ showString "Expected:"  , prt 0 expected, doc $ showString "\n"
+    , doc $ showString "Actual: "   , prt 0 actual
+    ]
diff --git a/src/TypeCheckerIr.hs b/src/TypeCheckerIr.hs
new file mode 100644
index 0000000..f6e3ec6
--- /dev/null
+++ b/src/TypeCheckerIr.hs
@@ -0,0 +1,100 @@
+{-# LANGUAGE LambdaCase #-}
+
+module TypeCheckerIr
+  ( module Grammar.Abs
+  , module TypeCheckerIr
+  ) where
+
+import           Grammar.Abs   (Ident (..), Type (..))
+import           Grammar.Print
+import           Prelude
+import qualified Prelude       as C (Eq, Ord, Read, Show)
+
+newtype Program = Program [Bind]
+  deriving (C.Eq, C.Ord, C.Show, C.Read)
+
+data Exp
+    = EId  Id
+    | EInt Integer
+    | ELet Bind Exp
+    | EApp Type Exp Exp
+    | EAdd Type Exp Exp
+    | EAbs Type Id  Exp
+      deriving (C.Eq, C.Ord, C.Show, C.Read)
+
+type Id = (Ident, Type)
+
+data Bind = Bind Id [Id] Exp
+    deriving (C.Eq, C.Ord, C.Show, C.Read)
+
+instance Print Program where
+    prt i (Program sc) = prPrec i 0 $ prt 0 sc
+
+instance Print Bind where
+    prt i (Bind name@(n, _) parms rhs) = prPrec i 0 $ concatD
+        [ prtId 0 name
+        , doc $ showString ";"
+        , prt 0 n
+        , prtIdPs 0 parms
+        , doc $ showString "="
+        , prt 0 rhs
+        ]
+
+instance Print [Bind] where
+  prt _ []     = concatD []
+  prt _ [x]    = concatD [prt 0 x]
+  prt _ (x:xs) = concatD [prt 0 x, doc (showString ";"), prt 0 xs]
+
+prtIdPs :: Int -> [Id] -> Doc
+prtIdPs i = prPrec i 0 . concatD . map (prtIdP i)
+
+prtId :: Int -> Id -> Doc
+prtId i (name, t) = prPrec i 0 $ concatD
+    [ prt 0 name
+    , doc $ showString ":"
+    , prt 0 t
+    ]
+
+prtIdP :: Int -> Id -> Doc
+prtIdP i (name, t) = prPrec i 0 $ concatD
+    [ doc $ showString "("
+    , prt 0 name
+    , doc $ showString ":"
+    , prt 0 t
+    , doc $ showString ")"
+    ]
+
+
+instance Print Exp where
+  prt i = \case
+      EId  n       -> prPrec i 3 $ concatD [prtIdP 0 n]
+      EInt i1      -> prPrec i 3 $ concatD [prt 0 i1]
+      ELet bs e    -> prPrec i 3 $ concatD
+                          [ doc $ showString "let"
+                          , prt 0 bs
+                          , doc $ showString "in"
+                          , prt 0 e
+                          ]
+      EApp t e1 e2 -> prPrec i 2 $ concatD
+                          [ doc $ showString "@"
+                          , prt 0 t
+                          , prt 2 e1
+                          , prt 3 e2
+                          ]
+      EAdd t e1 e2 -> prPrec i 1 $ concatD
+                          [ doc $ showString "@"
+                          , prt 0 t
+                          , prt 1 e1
+                          , doc $ showString "+"
+                          , prt 2 e2
+                          ]
+      EAbs t n  e  -> prPrec i 0 $ concatD
+                          [ doc $ showString "@"
+                          , prt 0 t
+                          , doc $ showString "\\"
+                          , prtIdP 0 n
+                          , doc $ showString "."
+                          , prt 0 e
+                          ]
+
+
diff --git a/test_program b/test_program
deleted file mode 100644
index 83f3e9a..0000000
--- a/test_program
+++ /dev/null
@@ -1,5 +0,0 @@
-
-
-
-
-main = (\x -> x + x + 3) ((\x -> x) 2)