diff --git a/src/bytecode.rs b/src/bytecode.rs
index 52a07ae..531eb0b 100644
--- a/src/bytecode.rs
+++ b/src/bytecode.rs
@@ -20,10 +20,14 @@
 //! to the length before the call. This means the interpreter has to do some bookkeeping, but it has
 //! to do that anyways.
 //!
+//! It is the compilers job to generate the correct loading of the arguments and assure that the aritiy
+//! is correct before the `Call` instruction.
+//!
+//!
 //! # ABI
 //! Function arguments are passed on the stack and can be loaded just like local variables. They belong
 //! to the stack frame of the new function and are cleaned up after returning, leaving the return value where
-//! the stack frame was.
+//! the stack frame was
 //!
 //! When a call happens, the current stack offset is pushed onto the stack as a `Value::Native` and
 //! the element before it is stored as the new offset.
@@ -37,14 +41,14 @@
 //! returned value.
 //!
 //! ```text
-//!  old stack offset ╮     ╭ Parameters ╮       ╭ local
-//!                   v     v            v       v
-//! ───────┬────────────┬───────────┬──────────┬─────────╮
-//! Num(6) │ Native(20) │   Num(5)  │  Num(6)  │  Num(5) │
-//! ───────┴────────────┴───────────┴──────────┴─────────╯
-//!        ╰────────────────────────────────────────────────── current stack frame
-//!  ^                  ^
-//!  ╰─ old local       ╰╮      
+//!  old stack offset ╮     old *mut FnBlock ╮     ╭ Parameters ╮       ╭ local
+//!                   v                      v     v            v       v
+//! ───────┬─────────────┬────────────┬──────────┬─────────┬──────────┬─────────╮
+//! Num(6) │ NativeU(20) │ NativeU(4) │  Ptr     │ Num(5)  │  Num(6)  │  Num(5) │
+//! ───────┴─────────────┴────────────┴──────────┴─────────┴──────────┴─────────╯
+//!  ^     ╰──────────────────────────────────────────────────────────────────── current stack frame
+//!  │                  ^      ^
+//!  ╰─ old local       ╰╮     ╰─ old PC
 //!                      │
 //!                      │
 //! Vm                   │
diff --git a/src/compile.rs b/src/compile.rs
index af2b5e4..0e6fce5 100644
--- a/src/compile.rs
+++ b/src/compile.rs
@@ -152,7 +152,7 @@ impl<'bc, 'gc> Compiler<'bc, 'gc> {
         Ok(())
     }
 
-    fn compile_fn_decl(&mut self, _: &FnDecl) -> CResult {
+    fn compile_fn_decl(&mut self, decl: &FnDecl) -> CResult {
         todo!()
     }
 
@@ -415,13 +415,13 @@ impl<'bc, 'gc> Compiler<'bc, 'gc> {
         block.stack_sizes.last().copied().unwrap_or(0)
     }
 
-    fn change_instr(&mut self, index: usize, instr: Instr) {
+    fn change_instr(&mut self, index: usize, instr: Instr<'bc>) {
         let block = &mut self.blocks[self.current_block];
         block.code[index] = instr;
     }
 
     /// Pushes an instruction and returns the index of the new instruction
-    fn push_instr(&mut self, instr: Instr, stack_change: StackChange, span: Span) -> usize {
+    fn push_instr(&mut self, instr: Instr<'bc>, stack_change: StackChange, span: Span) -> usize {
         let block = &mut self.blocks[self.current_block];
         let stack_top = block.stack_sizes.last().copied().unwrap_or(0);
         let new_stack_top = stack_top as isize + stack_change.as_isize();
diff --git a/src/vm.rs b/src/vm.rs
index 93df565..220b22e 100644
--- a/src/vm.rs
+++ b/src/vm.rs
@@ -3,6 +3,7 @@ use crate::gc::{Object, RtAlloc, Symbol};
 use crate::Config;
 use std::fmt::{Debug, Display, Formatter};
 use std::io::{Read, Write};
+use std::ptr::NonNull;
 
 type VmError = &'static str;
 type VmResult = Result<(), VmError>;
@@ -13,7 +14,6 @@ pub fn execute<'bc>(
     cfg: &mut Config,
 ) -> Result<(), VmError> {
     let mut vm = Vm {
-        _blocks: bytecode,
         current: bytecode.first().ok_or("no bytecode found")?,
         pc: 0,
         stack: Vec::with_capacity(1024 << 5),
@@ -40,10 +40,15 @@ pub enum Value {
     Array,
     /// A map from string to value
     Object(Object),
-    /// A value that is stored by the vm for bookkeeping and should never be accessed for anythign else
-    Native(usize),
+    /// A value that is stored by the vm for bookkeeping and should never be accessed for anything else
+    NativeU(usize),
+    /// A function
+    Fn(Ptr),
 }
 
+#[derive(Debug, Clone, Copy)]
+pub struct Ptr(NonNull<()>);
+
 const _: () = _check_val_size();
 const fn _check_val_size() {
     if std::mem::size_of::<Value>() != 24 {
@@ -55,14 +60,16 @@ const TRUE: Value = Value::Bool(true);
 const FALSE: Value = Value::Bool(false);
 
 struct Vm<'bc, 'io> {
-    _blocks: &'bc [FnBlock<'bc>],
-    current: &'bc FnBlock<'bc>,
+    // -- global
     _alloc: RtAlloc,
-    /// Index of the instruction currently being executed
-    pc: usize,
     stack: Vec<Value>,
     stdout: &'io mut dyn Write,
     step: bool,
+
+    // -- local to the current function
+    current: &'bc FnBlock<'bc>,
+    /// Index of the instruction currently being executed
+    pc: usize,
 }
 
 impl<'bc> Vm<'bc, '_> {
@@ -179,6 +186,7 @@ impl<'bc> Vm<'bc, '_> {
             }
             Instr::Jmp(pos) => self.pc = (self.pc as isize + pos) as usize,
             Instr::Call(_) => todo!(),
+            Instr::Return => todo!(),
             Instr::ShrinkStack(size) => {
                 assert!(self.stack.len() >= size);
                 let new_len = self.stack.len() - size;
@@ -232,7 +240,15 @@ impl Display for Value {
             Value::String(str) => f.write_str(str.as_str()),
             Value::Array => todo!(),
             Value::Object(_) => todo!(),
-            Value::Native(_) => panic!("Called display on native value!"),
+            Value::NativeU(_) => panic!("Called display on native value!"),
+            Value::Fn(_) => f.write_str("[function]"),
         }
     }
 }
+
+#[cfg(feature = "pretty")]
+impl debug2::Debug for Ptr {
+    fn fmt(&self, f: &mut debug2::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Ptr").finish()
+    }
+}