Merge remote-tracking branch 'origin/wip-close' into main

4 files changed, 424 insertions, 86 deletions

diff --git a/src/compiler.rs b/src/compiler.rs
index 1a6cfc6..70c9a51 100644
--- a/src/compiler.rs
+++ b/src/compiler.rs
@@ -1,12 +1,13 @@
 use std::path::{Path, PathBuf};
 use std::rc::Rc;
+use std::cell::RefCell;
 
 use crate::error::{Error, ErrorKind};
 use crate::tokenizer::{Token, TokenStream};
 use crate::vm::{Value, Block, Op};
 
 macro_rules! nextable_enum {
-    ( $name:ident { $( $thing:ident ),* } ) => {
+    ( $name:ident { $( $thing:ident ),* $( , )? } ) => {
         #[derive(PartialEq, PartialOrd, Clone, Copy, Debug)]
         enum $name {
             $( $thing, )*
@@ -43,7 +44,7 @@ nextable_enum!(Prec {
     Bool,
     Comp,
     Term,
-    Factor
+    Factor,
 });
 
 #[derive(Debug, Clone)]
@@ -79,13 +80,20 @@ impl From<&Value> for Type {
             Value::Float(_) => Type::Float,
             Value::Bool(_) => Type::Bool,
             Value::String(_) => Type::String,
-            Value::Function(block) => block.ty.clone(),
+            Value::Function(_, block) => block.borrow().ty.clone(),
             _ => Type::Void,
         }
     }
 }
 
 impl Type {
+    pub fn is_unkown(&self) -> bool {
+        match self {
+            Type::UnknownType => true,
+            _ => false,
+        }
+    }
+
     pub fn as_value(&self) -> Value {
         match self {
             Type::Void => Value::Nil,
@@ -94,24 +102,68 @@ impl Type {
             Type::Float => Value::Float(1.0),
             Type::Bool => Value::Bool(true),
             Type::String => Value::String(Rc::new("".to_string())),
-            Type::Function(_, _) => Value::Function(Rc::new(Block::from_type(self))),
+            Type::Function(_, _) => Value::Function(
+                Vec::new(),
+                Rc::new(RefCell::new(Block::from_type(self)))),
         }
     }
 }
 
+#[derive(Clone)]
 struct Variable {
     name: String,
     typ: Type,
     scope: usize,
+    slot: usize,
+
+    outer_slot: usize,
+    outer_upvalue: bool,
+
     active: bool,
+    upvalue: bool,
+    captured: bool,
 }
 
 struct Frame {
     stack: Vec<Variable>,
+    upvalues: Vec<Variable>,
     scope: usize,
     variables_below: usize,
 }
 
+impl Frame {
+    fn find_local(&self, name: &str) -> Option<Variable> {
+        for var in self.stack.iter().rev() {
+            if var.name == name && var.active {
+                return Some(var.clone());
+            }
+        }
+        None
+    }
+
+    fn find_upvalue(&self, name: &str) -> Option<Variable> {
+        for var in self.upvalues.iter().rev() {
+            if var.name == name && var.active {
+                return Some(var.clone());
+            }
+        }
+        None
+    }
+
+    fn add_upvalue(&mut self, variable: Variable) -> Variable {
+        let new_variable = Variable {
+            outer_upvalue: variable.upvalue,
+            outer_slot: variable.slot,
+            slot: self.upvalues.len(),
+            active: true,
+            upvalue: true,
+            ..variable
+        };
+        self.upvalues.push(new_variable.clone());
+        new_variable
+    }
+}
+
 struct Compiler {
     curr: usize,
     tokens: TokenStream,
@@ -122,7 +174,7 @@ struct Compiler {
     panic: bool,
     errors: Vec<Error>,
 
-    blocks: Vec<Rc<Block>>,
+    blocks: Vec<Rc<RefCell<Block>>>,
 }
 
 macro_rules! push_frame {
@@ -130,6 +182,7 @@ macro_rules! push_frame {
         {
             $compiler.frames.push(Frame {
                 stack: Vec::new(),
+                upvalues: Vec::new(),
                 scope: 0,
                 variables_below: $compiler.frame().variables_below + $compiler.stack().len(),
             });
@@ -154,8 +207,13 @@ macro_rules! push_scope {
         $code;
 
         $compiler.frame_mut().scope -= 1;
-        for _ in ss..$compiler.stack().len() {
-            $block.add(Op::Pop, $compiler.line());
+
+        for var in $compiler.frame().stack[ss..$compiler.stack().len()].iter().rev() {
+            if var.captured {
+                $block.add(Op::PopUpvalue, $compiler.line());
+            } else {
+                $block.add(Op::Pop, $compiler.line());
+            }
         }
         $compiler.stack_mut().truncate(ss);
     };
@@ -170,6 +228,7 @@ impl Compiler {
 
             frames: vec![Frame {
                 stack: Vec::new(),
+                upvalues: Vec::new(),
                 scope: 0,
                 variables_below: 0,
             }],
@@ -311,8 +370,6 @@ impl Compiler {
                 | Token::NotEqual
                 => self.binary(block),
 
-            Token::LeftParen => self.call(block),
-
             _ => { return false; },
         }
         return true;
@@ -388,16 +445,36 @@ impl Compiler {
         }
     }
 
-    fn find_local(&self, name: &str, _block: &Block) -> Option<(usize, Type, usize)> {
-        let frame = self.frame();
-        for (slot, var) in frame.stack.iter().enumerate().rev() {
-            if var.name == name && var.active {
-                return Some((slot, var.typ.clone(), var.scope));
+    fn find_and_capture_variable<'a, I>(name: &str, mut iterator: I) -> Option<Variable>
+    where I: Iterator<Item = &'a mut Frame> {
+        if let Some(frame) = iterator.next() {
+            if let Some(res) = frame.find_local(name) {
+                frame.stack[res.slot].captured = true;
+                return Some(res);
+            }
+            if let Some(res) = frame.find_upvalue(name) {
+                return Some(res);
+            }
+
+            if let Some(res) = Self::find_and_capture_variable(name, iterator) {
+                return Some(frame.add_upvalue(res));
             }
         }
         None
     }
 
+    fn find_variable(&mut self, name: &str) -> Option<Variable> {
+        if let Some(res) = self.frame().find_local(name) {
+            return Some(res);
+        }
+
+        if let Some(res) = self.frame().find_upvalue(name) {
+            return Some(res);
+        }
+
+        return Self::find_and_capture_variable(name, self.frames.iter_mut().rev());
+    }
+
     fn call(&mut self, block: &mut Block) {
         expect!(self, Token::LeftParen, "Expected '(' at start of function call.");
 
@@ -423,17 +500,15 @@ impl Compiler {
         }
 
         block.add(Op::Call(arity), self.line());
-
-        for _ in 0..arity {
-            block.add(Op::Pop, self.line());
-        }
     }
 
     fn function(&mut self, block: &mut Block) {
         expect!(self, Token::Fn, "Expected 'fn' at start of function.");
 
-        let name = if !self.stack()[self.stack().len() - 1].active {
-            &self.stack()[self.stack().len() - 1].name
+        let top = self.stack().len() - 1;
+        let name = if !self.stack()[top].active {
+            self.stack_mut()[top].active = true;
+            &self.stack()[top].name
         } else {
             "anonumus function"
         };
@@ -441,6 +516,7 @@ impl Compiler {
         let mut args = Vec::new();
         let mut return_type = Type::Void;
         let mut function_block = Block::new(name, &self.current_file, self.line());
+
         let _ret = push_frame!(self, function_block, {
             loop {
                 match self.peek() {
@@ -479,35 +555,60 @@ impl Compiler {
             }
 
             self.scope(&mut function_block);
+
+            for var in self.frame().upvalues.iter() {
+                function_block.ups.push((var.outer_slot, var.outer_upvalue, var.typ.clone()));
+            }
         });
 
-        if !matches!(function_block.last_op(), Some(&Op::Return)) {
+        for op in function_block.ops.iter().rev() {
+            match op {
+                Op::Pop | Op::PopUpvalue => {}
+                Op::Return => { break; } ,
+                _ => {
+                    function_block.add(Op::Constant(Value::Nil), self.line());
+                    function_block.add(Op::Return, self.line());
+                    break;
+                }
+            }
+        }
+
+        if function_block.ops.is_empty() {
             function_block.add(Op::Constant(Value::Nil), self.line());
             function_block.add(Op::Return, self.line());
         }
 
         function_block.ty = Type::Function(args, Box::new(return_type));
-        let function_block = Rc::new(function_block);
+        let function_block = Rc::new(RefCell::new(function_block));
+
 
-        block.add(Op::Constant(Value::Function(Rc::clone(&function_block))), self.line());
+        let func = Op::Constant(Value::Function(Vec::new(), Rc::clone(&function_block)));
+        block.add(func, self.line());
         self.blocks.push(function_block);
     }
 
     fn variable_expression(&mut self, block: &mut Block) {
         let name = match self.eat() {
             Token::Identifier(name) => name,
-            __ => unreachable!(),
+            _ => unreachable!(),
         };
-        if let Some((slot, _, _)) = self.find_local(&name, block) {
-            block.add(Op::ReadLocal(slot), self.line());
+        if let Some(var) = self.find_variable(&name) {
+            if var.upvalue {
+                block.add(Op::ReadUpvalue(var.slot), self.line());
+            } else {
+                block.add(Op::ReadLocal(var.slot), self.line());
+            }
+            if self.peek() == Token::LeftParen {
+                self.call(block);
+            }
         } else {
             error!(self, format!("Using undefined variable {}.", name));
         }
     }
 
-    fn define_variable(&mut self, name: &str, typ: Type, block: &mut Block) -> Result<usize, ()> {
-        if let Some((_, _, level)) = self.find_local(&name, block) {
-            if level == self.frame().scope {
+    fn define_variable(&mut self, name: &str, typ: Type, _block: &mut Block) -> Result<usize, ()> {
+        if let Some(var) = self.find_variable(&name) {
+            if var.scope == self.frame().scope {
                 error!(self, format!("Multiple definitions of {} in this block.", name));
                 return Err(());
             }
@@ -517,9 +618,14 @@ impl Compiler {
         let scope = self.frame().scope;
         self.stack_mut().push(Variable {
             name: String::from(name),
+            captured: false,
+            outer_upvalue: false,
+            outer_slot: 0,
+            slot,
             typ,
             scope,
-            active: false
+            active: false,
+            upvalue: false,
         });
         Ok(slot)
     }
@@ -535,9 +641,13 @@ impl Compiler {
     }
 
     fn assign(&mut self, name: &str, block: &mut Block) {
-        if let Some((slot, _, _)) = self.find_local(&name, block) {
+        if let Some(var) = self.find_variable(&name) {
             self.expression(block);
-            block.add(Op::Assign(slot), self.line());
+            if var.upvalue {
+                block.add(Op::AssignUpvalue(var.slot), self.line());
+            } else {
+                block.add(Op::AssignLocal(var.slot), self.line());
+            }
         } else {
             error!(self, format!("Using undefined variable {}.", name));
         }
@@ -743,12 +853,17 @@ impl Compiler {
 
     }
 
-    pub fn compile(&mut self, name: &str, file: &Path) -> Result<Vec<Rc<Block>>, Vec<Error>> {
+    pub fn compile(&mut self, name: &str, file: &Path) -> Result<Vec<Rc<RefCell<Block>>>, Vec<Error>> {
         self.stack_mut().push(Variable {
             name: String::from("/main/"),
             typ: Type::Void,
+            outer_upvalue: false,
+            outer_slot: 0,
+            slot: 0,
             scope: 0,
             active: false,
+            captured: false,
+            upvalue: false,
         });
 
         let mut block = Block::new(name, file, 0);
@@ -760,7 +875,7 @@ impl Compiler {
         block.add(Op::Return, self.line());
         block.ty = Type::Function(Vec::new(), Box::new(Type::Void));
 
-        self.blocks.insert(0, Rc::new(block));
+        self.blocks.insert(0, Rc::new(RefCell::new(block)));
 
         if self.errors.is_empty() {
             Ok(self.blocks.clone())
@@ -770,6 +885,6 @@ impl Compiler {
     }
 }
 
-pub fn compile(name: &str, file: &Path, tokens: TokenStream) -> Result<Vec<Rc<Block>>, Vec<Error>> {
+pub fn compile(name: &str, file: &Path, tokens: TokenStream) -> Result<Vec<Rc<RefCell<Block>>>, Vec<Error>> {
     Compiler::new(file, tokens).compile(name, file)
 }
diff --git a/src/lib.rs b/src/lib.rs
index 82905de..e83d11f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -169,7 +169,7 @@ mod tests {
         simplest: "f := fn {}
                    f()",
         param_1: "f := fn a: int {}
-                f(1)",
+                  f(1)",
         return_1: "f := fn -> int {
                      ret 1
                    }
@@ -222,7 +222,55 @@ mod tests {
                      }
                      1 + f(2, 3) <=> 6
                      2 * f(2, 3) <=> 10
-                     f(2, 3) - (2 + 3) <=> 0"
+                     f(2, 3) - (2 + 3) <=> 0",
+        factorial: "factorial : fn int -> int = fn n: int -> int {
+                      if n <= 1 {
+                        ret 1
+                      }
+                      ret n * factorial(n - 1)
+                    }
+                    factorial(5) <=> 120
+                    factorial(6) <=> 720
+                    factorial(12) <=> 479001600",
+
+        returning_closures: "
+f : fn -> fn -> int = fn -> fn -> int {
+    x : int = 0
+    f := fn -> int {
+        x = x + 1
+        ret x
+    }
+    f() <=> 1
+    ret f
+}
+
+a := f()
+b := f()
+
+a() <=> 2
+a() <=> 3
+
+b() <=> 2
+b() <=> 3
+
+a() <=> 4
+"
+
+        //TODO this tests doesn't terminate in proper time if we print blocks and ops
+                    /*
+        fibonacci: "fibonacci : fn int -> int = fn n: int -> int {
+                      if n == 0 {
+                        ret 0
+                      } else if n == 1 {
+                        ret 1
+                      } else if n < 0 {
+                        <!>
+                      }
+                      ret fibonacci(n - 1) + fibonacci(n - 2)
+                    }
+                    fibonacci(10) <=> 55
+                    fibonacci(20) <=> 6765"
+                    */
     );
 
     test_file!(scoping, "tests/scoping.tdy");
diff --git a/src/vm.rs b/src/vm.rs
index 75a8eb1..5f7e0e3 100644
--- a/src/vm.rs
+++ b/src/vm.rs
@@ -1,8 +1,10 @@
 use owo_colors::OwoColorize;
 use std::collections::HashMap;
+use std::collections::hash_map::Entry;
 use std::fmt::Debug;
 use std::path::{Path, PathBuf};
 use std::rc::Rc;
+use std::cell::RefCell;
 
 use crate::compiler::Type;
 use crate::error::{Error, ErrorKind};
@@ -22,11 +24,53 @@ pub enum Value {
     Int(i64),
     Bool(bool),
     String(Rc<String>),
-    Function(Rc<Block>),
+    Function(Vec<Rc<RefCell<UpValue>>>, Rc<RefCell<Block>>),
     Unkown,
     Nil,
 }
 
+#[derive(Clone, Debug)]
+pub struct UpValue {
+    slot: usize,
+    value: Value,
+}
+
+impl UpValue {
+
+    fn new(value: usize) -> Self {
+        Self {
+            slot: value,
+            value: Value::Nil,
+        }
+    }
+
+    fn get(&self, stack: &[Value]) -> Value {
+        if self.is_closed() {
+            self.value.clone()
+        } else {
+            stack[self.slot].clone()
+        }
+    }
+
+    fn set(&mut self, stack: &mut [Value], value: Value) {
+        if self.is_closed() {
+            self.value = value;
+        } else {
+            stack[self.slot] = value;
+        }
+    }
+
+
+    fn is_closed(&self) -> bool {
+        self.slot == 0
+    }
+
+    fn close(&mut self, value: Value) {
+        self.slot = 0;
+        self.value = value;
+    }
+}
+
 impl Debug for Value {
     fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
@@ -34,7 +78,7 @@ impl Debug for Value {
             Value::Int(i) => write!(fmt, "(int {})", i),
             Value::Bool(b) => write!(fmt, "(bool {})", b),
             Value::String(s) => write!(fmt, "(string \"{}\")", s),
-            Value::Function(block) => write!(fmt, "(fn {}: {:?})", block.name, block.ty),
+            Value::Function(_, block) => write!(fmt, "(fn {}: {:?})", block.borrow().name, block.borrow().ty),
             Value::Unkown => write!(fmt, "(unkown)"),
             Value::Nil => write!(fmt, "(nil)"),
         }
@@ -57,7 +101,7 @@ impl Value {
             Value::Int(_) => Type::Int,
             Value::Bool(_) => Type::Bool,
             Value::String(_) => Type::String,
-            Value::Function(block) => block.ty.clone(),
+            Value::Function(_, block) => block.borrow().ty.clone(),
             Value::Unkown => Type::UnknownType,
             Value::Nil => Type::Void,
         }
@@ -69,6 +113,7 @@ pub enum Op {
     Illegal,
 
     Pop,
+    PopUpvalue,
     Constant(Value),
 
     Add,
@@ -92,7 +137,10 @@ pub enum Op {
     Unreachable,
 
     ReadLocal(usize),
-    Assign(usize),
+    AssignLocal(usize),
+
+    ReadUpvalue(usize),
+    AssignUpvalue(usize),
 
     Define(Type),
 
@@ -105,6 +153,7 @@ pub enum Op {
 #[derive(Debug)]
 pub struct Block {
     pub ty: Type,
+    pub ups: Vec<(usize, bool, Type)>,
 
     pub name: String,
     pub file: PathBuf,
@@ -118,6 +167,7 @@ impl Block {
     pub fn new(name: &str, file: &Path, line: usize) -> Self {
         Self {
             ty: Type::Void,
+            ups: Vec::new(),
             name: String::from(name),
             file: file.to_owned(),
             ops: Vec::new(),
@@ -216,12 +266,14 @@ impl Block {
 #[derive(Debug)]
 struct Frame {
     stack_offset: usize,
-    block: Rc<Block>,
+    block: Rc<RefCell<Block>>,
     ip: usize,
 }
 
 #[derive(Debug)]
 pub struct VM {
+    upvalues: HashMap<usize, Rc<RefCell<UpValue>>>,
+
     stack: Vec<Value>,
     frames: Vec<Frame>,
     print_blocks: bool,
@@ -236,6 +288,7 @@ enum OpResult {
 impl VM {
     pub fn new() -> Self {
         Self {
+            upvalues: HashMap::new(),
             stack: Vec::new(),
             frames: Vec::new(),
             print_blocks: false,
@@ -253,6 +306,20 @@ impl VM {
         self
     }
 
+    fn drop_upvalue(&mut self, slot: usize, value: Value) {
+        if let Entry::Occupied(entry) = self.upvalues.entry(slot) {
+            entry.get().borrow_mut().close(value);
+            entry.remove();
+        } else {
+            unreachable!();
+        }
+    }
+
+    fn find_upvalue(&mut self, slot: usize) -> &mut Rc<RefCell<UpValue>> {
+        self.upvalues.entry(slot).or_insert(
+            Rc::new(RefCell::new(UpValue::new(slot))))
+    }
+
     fn pop(&mut self) -> Value {
         self.stack.pop().unwrap()
     }
@@ -277,17 +344,17 @@ impl VM {
         &mut self.frames[last]
     }
 
-    fn op(&self) -> &Op {
+    fn op(&self) -> Op {
         let ip = self.frame().ip;
-        &self.frame().block.ops[ip]
+        self.frame().block.borrow().ops[ip].clone()
     }
 
     fn error(&self, kind: ErrorKind, message: Option<String>) -> Error {
         let frame = self.frames.last().unwrap();
         Error {
             kind,
-            file: frame.block.file.clone(),
-            line: frame.block.line(frame.ip),
+            file: frame.block.borrow().file.clone(),
+            line: frame.block.borrow().line(frame.ip),
             message,
         }
     }
@@ -303,11 +370,38 @@ impl VM {
             }
 
             Op::Pop => {
-                self.stack.pop();
+                self.stack.pop().unwrap();
+            }
+
+            Op::PopUpvalue => {
+                let value = self.stack.pop().unwrap();
+                let slot = self.stack.len();
+                self.drop_upvalue(slot, value);
             }
 
             Op::Constant(value) => {
-                self.stack.push(value.clone());
+                let offset = self.frame().stack_offset;
+                let value = match value {
+                    Value::Function(_, block) => {
+                        let mut ups = Vec::new();
+                        for (slot, is_up, _) in block.borrow().ups.iter() {
+                            let up = if *is_up {
+                                if let Value::Function(local_ups, _) = &self.stack[offset] {
+                                    Rc::clone(&local_ups[*slot])
+                                } else {
+                                    unreachable!()
+                                }
+                            } else {
+                                let slot = self.frame().stack_offset + slot;
+                                Rc::clone(self.find_upvalue(slot))
+                            };
+                            ups.push(up);
+                        }
+                        Value::Function(ups, block)
+                    },
+                    _ => value.clone(),
+                };
+                self.stack.push(value);
             }
 
             Op::Neg => {
@@ -423,12 +517,33 @@ impl VM {
                 self.stack.push(Value::Bool(true));
             }
 
+            Op::ReadUpvalue(slot) => {
+                let offset = self.frame().stack_offset;
+                let value = match &self.stack[offset] {
+                    Value::Function(ups, _) => {
+                        ups[slot].borrow().get(&self.stack)
+                    }
+                    _ => unreachable!(),
+                };
+                self.stack.push(value);
+            }
+
+            Op::AssignUpvalue(slot) => {
+                let offset = self.frame().stack_offset;
+                let value = self.stack.pop().unwrap();
+                let slot = match &self.stack[offset] {
+                    Value::Function(ups, _) => Rc::clone(&ups[slot]),
+                    _ => unreachable!(),
+                };
+                slot.borrow_mut().set(&mut self.stack, value);
+            }
+
             Op::ReadLocal(slot) => {
                 let slot = self.frame().stack_offset + slot;
                 self.stack.push(self.stack[slot].clone());
             }
 
-            Op::Assign(slot) => {
+            Op::AssignLocal(slot) => {
                 let slot = self.frame().stack_offset + slot;
                 self.stack[slot] = self.stack.pop().unwrap();
             }
@@ -438,16 +553,18 @@ impl VM {
             Op::Call(num_args) => {
                 let new_base = self.stack.len() - 1 - num_args;
                 match &self.stack[new_base] {
-                    Value::Function(block) => {
-                        let args = block.args();
+                    Value::Function(_, block) => {
+                        let inner = block.borrow();
+                        let args = inner.args();
                         if args.len() != num_args {
                             error!(self,
                                 ErrorKind::InvalidProgram,
                                 format!("Invalid number of arguments, got {} expected {}.",
                                     num_args, args.len()));
                         }
+
                         if self.print_blocks {
-                            block.debug_print();
+                            inner.debug_print();
                         }
                         self.frames.push(Frame {
                             stack_offset: new_base,
@@ -472,6 +589,13 @@ impl VM {
                     return Ok(OpResult::Done);
                 } else {
                     self.stack[last.stack_offset] = self.stack.pop().unwrap();
+                    for slot in last.stack_offset+1..self.stack.len() {
+                        if self.upvalues.contains_key(&slot) {
+                            let value = self.stack[slot].clone();
+                            self.drop_upvalue(slot, value);
+                        }
+                    }
+                    self.stack.truncate(last.stack_offset + 1);
                 }
             }
         }
@@ -491,16 +615,16 @@ impl VM {
         println!("]");
 
         println!("{:5} {:05} {:?}",
-            self.frame().block.line(self.frame().ip).red(),
+            self.frame().block.borrow().line(self.frame().ip).red(),
             self.frame().ip.blue(),
-            self.frame().block.ops[self.frame().ip]);
+            self.frame().block.borrow().ops[self.frame().ip]);
     }
 
-    pub fn run(&mut self, block: Rc<Block>) -> Result<(), Error>{
+    pub fn run(&mut self, block: Rc<RefCell<Block>>) -> Result<(), Error>{
         self.stack.clear();
         self.frames.clear();
 
-        self.stack.push(Value::Function(Rc::clone(&block)));
+        self.stack.push(Value::Function(Vec::new(), Rc::clone(&block)));
 
         self.frames.push(Frame {
             stack_offset: 0,
@@ -510,7 +634,7 @@ impl VM {
 
         if self.print_blocks {
             println!("\n    [[{}]]\n", "RUNNING".red());
-            self.frame().block.debug_print();
+            self.frame().block.borrow().debug_print();
         }
 
         loop {
@@ -518,7 +642,7 @@ impl VM {
                 self.print_stack()
             }
 
-            if matches!(self.eval_op(self.op().clone())?, OpResult::Done) {
+            if matches!(self.eval_op(self.op())?, OpResult::Done) {
                 return Ok(());
             }
         }
@@ -530,9 +654,65 @@ impl VM {
 
             Op::Jmp(_line) => {}
 
+            Op::Constant(ref value) => {
+                match value.clone() {
+                    Value::Function(_, block) => {
+                        self.stack.push(Value::Function(Vec::new(), block.clone()));
+
+                        let mut types = Vec::new();
+                        for (slot, is_up, _) in block.borrow().ups.iter() {
+                            if *is_up {
+                                types.push(Type::Void);
+                            } else {
+                                types.push(self.stack[*slot].as_type());
+                            }
+                        }
+
+                        let mut block_mut = block.borrow_mut();
+                        for (i, (_, is_up, ty)) in block_mut.ups.iter_mut().enumerate() {
+                            if *is_up { continue; }
+
+                            let suggestion = &types[i];
+                            if ty.is_unkown() {
+                                *ty = suggestion.clone();
+                            } else {
+                                if ty != suggestion {
+                                    error!(self,
+                                           ErrorKind::TypeError(op.clone(),
+                                                    vec![ty.clone(), suggestion.clone()]),
+                                           "Failed to infer type.".to_string());
+                                }
+                            }
+                        };
+                    },
+                    _ => {
+                        self.stack.push(value.clone());
+                    }
+                }
+            }
+
+            Op::PopUpvalue => {
+                self.stack.pop().unwrap();
+            }
+
+            Op::ReadUpvalue(slot) => {
+                let value = self.frame().block.borrow().ups[slot].2.as_value();
+                self.stack.push(value);
+            }
+
+            Op::AssignUpvalue(slot) => {
+                let var = self.frame().block.borrow().ups[slot].2.clone();
+                let up = self.stack.pop().unwrap().as_type();
+                if var != up {
+                    error!(self, ErrorKind::TypeError(op, vec![var, up]),
+                                  "Incorrect type for upvalue.".to_string());
+                }
+            }
+
             Op::Return => {
                 let a = self.stack.pop().unwrap();
-                let ret = self.frame().block.ret();
+                let inner = self.frame().block.borrow();
+                let ret = inner.ret();
                 if a.as_type() != *ret {
                     error!(self, ErrorKind::TypeError(op, vec![a.as_type(),
                                                                ret.clone()]),
@@ -563,9 +743,10 @@ impl VM {
 
             Op::Call(num_args) => {
                 let new_base = self.stack.len() - 1 - num_args;
-                match &self.stack[new_base] {
-                    Value::Function(block) => {
-                        let args = block.args();
+                match self.stack[new_base].clone() {
+                    Value::Function(_, block) => {
+                        let inner = block.borrow();
+                        let args = inner.args();
                         if args.len() != num_args {
                             error!(self,
                                 ErrorKind::InvalidProgram,
@@ -582,7 +763,9 @@ impl VM {
                                     args, stack_args));
                         }
 
-                        self.stack[new_base] = block.ret().as_value();
+                        self.stack[new_base] = block.borrow().ret().as_value();
+
+                        self.stack.truncate(new_base + 1);
                     },
                     _ => {
                         error!(self,
@@ -607,30 +790,30 @@ impl VM {
         Ok(())
     }
 
-    fn typecheck_block(&mut self, block: Rc<Block>) -> Vec<Error> {
+    fn typecheck_block(&mut self, block: Rc<RefCell<Block>>) -> Vec<Error> {
         self.stack.clear();
         self.frames.clear();
 
-        self.stack.push(Value::Function(Rc::clone(&block)));
-        for arg in block.args() {
+        self.stack.push(Value::Function(Vec::new(), Rc::clone(&block)));
+        for arg in block.borrow().args() {
             self.stack.push(arg.as_value());
         }
 
         self.frames.push(Frame {
             stack_offset: 0,
-            block: block,
+            block,
             ip: 0
         });
 
         if self.print_blocks {
             println!("\n    [[{}]]\n", "TYPECHECK".purple());
-            self.frame().block.debug_print();
+            self.frame().block.borrow().debug_print();
         }
 
         let mut errors = Vec::new();
         loop {
             let ip = self.frame().ip;
-            if ip >= self.frame().block.ops.len() {
+            if ip >= self.frame().block.borrow().ops.len() {
                 break;
             }
 
@@ -638,7 +821,7 @@ impl VM {
                 self.print_stack()
             }
 
-            if let Err(e) = self.check_op(self.op().clone()) {
+            if let Err(e) = self.check_op(self.op()) {
                 errors.push(e);
                 self.frame_mut().ip += 1;
             }
@@ -651,7 +834,7 @@ impl VM {
         errors
     }
 
-    pub fn typecheck(&mut self, blocks: &Vec<Rc<Block>>) -> Result<(), Vec<Error>> {
+    pub fn typecheck(&mut self, blocks: &Vec<Rc<RefCell<Block>>>) -> Result<(), Vec<Error>> {
         let mut errors = Vec::new();
 
         for block in blocks.iter() {
diff --git a/tests/simple.tdy b/tests/simple.tdy
index f7929f4..28bd5e2 100644
--- a/tests/simple.tdy
+++ b/tests/simple.tdy
@@ -1,19 +1,11 @@
-a : fn int, int -> int = fn b: int, c: int -> int {
-   ret b + c
+fac : fn int -> int = fn a: int -> int {
+    if a <= 1 {
+        ret 1
+    }
+    b := fac(a - 1)
+    ret a * b
 }
-
-print a(1, 2) + 1
-
-b := fn c: fn int -> -> int {
-    c(2)
-    ret 1
-}
-
-c := fn a: int {
-    print a
-}
-
-b(c)
+print fac(5)
 
 // print b(fn a: int -> {
 //     print a