Introduce Value::Cell for mutable upvalues, allowing closures to

modify captured variables.
Implement `capture_upvalue` and `get_value`/`set_value` methods in the
`VM` to handle these mutable upvalues.

Refactor number parsing to support integers and floats

Separate the `TokenKind::Number` into `TokenKind::Integer` and
`TokenKind::Float`.
Update the lexer to distinguish between integer and float literals.
Update the parser to correctly map these new token kinds to their
respective `Value` types.

Add integration tests for parsing integers and floats, and for closure
modification of captured variables.

src/ast/lexer.rs

@@ -11,7 +11,8 @@ pub enum TokenKind {
     Quote, Backtick, Tilde, At,
     Identifier(Arc<str>),
     Keyword(Arc<str>),
-    Number(f64),
+    Integer(i64),
+    Float(f64),
     String(Arc<str>),
     EOF,
 }
@@ -69,8 +70,20 @@ impl<'a> Lexer<'a> {
             '"' => TokenKind::String(Arc::from(self.read_string()?)),
             c if c.is_ascii_digit() || (c == '-' && self.input.peek().is_some_and(|p| p.is_ascii_digit())) => {
                 let mut num_str = String::from(c);
-                num_str.push_str(&self.read_while(|c| c.is_ascii_digit() || c == '.'));
-                TokenKind::Number(num_str.parse().map_err(|_| "Invalid number format")?)
+                while let Some(&next) = self.peek() {
+                    if next.is_ascii_digit() || next == '.' {
+                        num_str.push(self.input.next().unwrap());
+                        self.col += 1;
+                    } else {
+                        break;
+                    }
+                }
+                
+                if num_str.contains('.') {
+                     TokenKind::Float(num_str.parse().map_err(|_| "Invalid float format")?)
+                } else {
+                     TokenKind::Integer(num_str.parse().map_err(|_| "Invalid integer format")?)
+                }
             }
             c if is_ident_start(c) => {
                 let mut id = String::from(c);

src/ast/parser.rs

@@ -51,7 +51,8 @@ impl<'a> Parser<'a> {
         let identity = Arc::new(NodeIdentity { location: token.location });
 
         let kind = match token.kind {
-            TokenKind::Number(n) => UntypedKind::Constant(Value::Float(n)),
+            TokenKind::Integer(n) => UntypedKind::Constant(Value::Int(n)),
+            TokenKind::Float(n) => UntypedKind::Constant(Value::Float(n)),
             TokenKind::String(s) => UntypedKind::Constant(Value::Text(s)),
             TokenKind::Keyword(k) => UntypedKind::Constant(Value::Keyword(Keyword::intern(&k))),
             TokenKind::Identifier(id) => {

src/ast/types.rs

@@ -68,6 +68,7 @@ pub enum Value {
     Record(Arc<HashMap<Keyword, Value>>),
     Function(Arc<dyn Fn(Vec<Value>) -> Value + Send + Sync>),
     Object(Arc<dyn Object>), // For compiled Closures and other opaque types
+    Cell(Arc<Mutex<Value>>), // Boxed value for captures
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
@@ -93,6 +94,7 @@ impl Value {
         match self {
             Value::Void => false,
             Value::Bool(b) => *b,
+            Value::Cell(c) => c.lock().unwrap().is_truthy(),
             _ => true,
         }
     }
@@ -109,6 +111,7 @@ impl Value {
             Value::Record(_) => StaticType::Record(Arc::new(BTreeMap::new())), // Empty for now
             Value::Function { .. } => StaticType::Any, // Dynamic function
             Value::Object(o) => StaticType::Object(o.type_name()),
+            Value::Cell(c) => c.lock().unwrap().static_type(),
         }
     }
 }
@@ -126,6 +129,7 @@ impl fmt::Display for Value {
             Value::Record(r) => write!(f, "<record[{}]>", r.len()),
             Value::Function(_) => write!(f, "<native fn>"),
             Value::Object(o) => write!(f, "<{}>", o.type_name()),
+            Value::Cell(c) => write!(f, "{}", c.lock().unwrap()),
         }
     }
 }

src/ast/vm.rs

@@ -7,7 +7,7 @@ use crate::ast::types::{Value, Object, StaticType};
 #[derive(Debug, Clone)]
 pub struct Closure {
     pub function_node: Arc<Node<BoundKind, StaticType>>,
-    pub upvalues: Vec<Value>,
+    pub upvalues: Vec<Arc<Mutex<Value>>>,
 }
 
 impl Object for Closure {
@@ -102,7 +102,7 @@ impl VM {
             BoundKind::Lambda { param_count: _, upvalues, body } => {
                 let mut captured = Vec::with_capacity(upvalues.len());
                 for addr in upvalues {
-                    captured.push(self.get_value(*addr)?);
+                    captured.push(self.capture_upvalue(*addr)?);
                 }
 
                 let closure = Closure {
@@ -151,13 +151,53 @@ impl VM {
         }
     }
 
+    fn capture_upvalue(&mut self, addr: Address) -> Result<Arc<Mutex<Value>>, String> {
+        match addr {
+            Address::Local(idx) => {
+                let frame = self.frames.last().ok_or("No call frame")?;
+                let abs_index = frame.stack_base + (idx as usize);
+                if abs_index < self.stack.len() {
+                    // Check if already boxed
+                    if let Value::Cell(cell) = &self.stack[abs_index] {
+                        Ok(cell.clone())
+                    } else {
+                        // Box it
+                        let val = self.stack[abs_index].clone();
+                        let cell = Arc::new(Mutex::new(val));
+                        self.stack[abs_index] = Value::Cell(cell.clone());
+                        Ok(cell)
+                    }
+                } else {
+                    Err(format!("Stack underflow capture local {}", idx))
+                }
+            },
+            Address::Upvalue(idx) => {
+                let frame = self.frames.last().ok_or("No call frame")?;
+                if let Some(closure) = &frame.closure {
+                    let idx = idx as usize;
+                    if idx < closure.upvalues.len() {
+                        Ok(closure.upvalues[idx].clone())
+                    } else {
+                        Err(format!("Upvalue access out of bounds capture {}", idx))
+                    }
+                } else {
+                    Err("Current frame has no closure".to_string())
+                }
+            },
+             Address::Global(_) => Err("Cannot capture global directly".to_string()),
+        }
+    }
+
     fn get_value(&self, addr: Address) -> Result<Value, String> {
         match addr {
             Address::Local(idx) => {
                 let frame = self.frames.last().ok_or("No call frame")?;
                 let abs_index = frame.stack_base + (idx as usize);
                 if abs_index < self.stack.len() {
-                    Ok(self.stack[abs_index].clone())
+                    match &self.stack[abs_index] {
+                        Value::Cell(cell) => Ok(cell.lock().unwrap().clone()),
+                        val => Ok(val.clone()),
+                    }
                 } else {
                     Err(format!("Stack underflow access local {}", idx))
                 }
@@ -176,7 +216,7 @@ impl VM {
                 if let Some(closure) = &frame.closure {
                     let idx = idx as usize;
                     if idx < closure.upvalues.len() {
-                        Ok(closure.upvalues[idx].clone())
+                        Ok(closure.upvalues[idx].lock().unwrap().clone())
                     } else {
                         Err(format!("Upvalue access out of bounds {}", idx))
                     }
@@ -192,14 +232,16 @@ impl VM {
             Address::Local(idx) => {
                 let frame = self.frames.last().ok_or("No call frame")?;
                 let abs_index = frame.stack_base + (idx as usize);
-                if abs_index >= self.stack.len() {
-                    if abs_index == self.stack.len() {
-                        self.stack.push(value);
-                    } else {
-                        return Err(format!("Stack gap write local {}", idx));
-                    }
+                if abs_index < self.stack.len() {
+                     if let Value::Cell(cell) = &self.stack[abs_index] {
+                        *cell.lock().unwrap() = value;
+                     } else {
+                        self.stack[abs_index] = value;
+                     }
+                } else if abs_index == self.stack.len() {
+                    self.stack.push(value);
                 } else {
-                    self.stack[abs_index] = value;
+                    return Err(format!("Stack gap write local {}", idx));
                 }
                 Ok(())
             },
@@ -212,7 +254,127 @@ impl VM {
                 globals[idx] = value;
                 Ok(())
             },
-            Address::Upvalue(_) => Err("Cannot assign to upvalue (Closure Upvalues are immutable)".to_string()),
+            Address::Upvalue(idx) => {
+                let frame = self.frames.last().ok_or("No call frame")?;
+                if let Some(closure) = &frame.closure {
+                    let idx = idx as usize;
+                    if idx < closure.upvalues.len() {
+                        *closure.upvalues[idx].lock().unwrap() = value;
+                        Ok(())
+                    } else {
+                        Err(format!("Upvalue assignment out of bounds {}", idx))
+                    }
+                } else {
+                    Err("Current frame has no closure".to_string())
+                }
+            },
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::ast::types::{SourceLocation, NodeIdentity};
+
+    fn make_dummy_identity() -> Arc<NodeIdentity> {
+        Arc::new(NodeIdentity {
+            location: SourceLocation { line: 0, col: 0 },
+        })
+    }
+
+    #[test]
+    fn test_capture_boxing_modification() {
+        // Goal:
+        // var x = 10; (Local 0)
+        // var f = lambda { x = 20; }; (Local 1)
+        // f();
+        // return x; -> Should be 20
+
+        let id = make_dummy_identity();
+
+        // 1. Define Lambda Body: x = 20 (Upvalue 0)
+        let lambda_body = Node {
+            identity: id.clone(),
+            ty: StaticType::Void,
+            kind: BoundKind::Set {
+                addr: Address::Upvalue(0),
+                value: Box::new(Node {
+                    identity: id.clone(),
+                    ty: StaticType::Int,
+                    kind: BoundKind::Constant(Value::Int(20)),
+                }),
+            },
+        };
+
+        // 2. Define Main Script
+        let root = Node {
+            identity: id.clone(),
+            ty: StaticType::Int,
+            kind: BoundKind::Block {
+                exprs: vec![
+                    // x = 10 (Local 0) - simulate definition by assignment to stack gap
+                    Node {
+                        identity: id.clone(),
+                        ty: StaticType::Int,
+                        kind: BoundKind::Set {
+                            addr: Address::Local(0),
+                            value: Box::new(Node {
+                                identity: id.clone(),
+                                ty: StaticType::Int,
+                                kind: BoundKind::Constant(Value::Int(10)),
+                            }),
+                        },
+                    },
+                    // f = lambda capturing x (Local 1)
+                    Node {
+                        identity: id.clone(),
+                        ty: StaticType::Any,
+                        kind: BoundKind::Set {
+                            addr: Address::Local(1),
+                            value: Box::new(Node {
+                                identity: id.clone(),
+                                ty: StaticType::Any,
+                                kind: BoundKind::Lambda {
+                                    param_count: 0,
+                                    upvalues: vec![Address::Local(0)], // Capture x
+                                    body: Arc::new(lambda_body),
+                                },
+                            }),
+                        },
+                    },
+                    // f()
+                    Node {
+                        identity: id.clone(),
+                        ty: StaticType::Void,
+                        kind: BoundKind::Call {
+                            callee: Box::new(Node {
+                                identity: id.clone(),
+                                ty: StaticType::Any,
+                                kind: BoundKind::Get(Address::Local(1)),
+                            }),
+                            args: vec![],
+                        },
+                    },
+                    // return x (Local 0)
+                    Node {
+                        identity: id.clone(),
+                        ty: StaticType::Int,
+                        kind: BoundKind::Get(Address::Local(0)),
+                    },
+                ],
+            },
+        };
+
+        let globals = Arc::new(Mutex::new(Vec::new()));
+        let mut vm = VM::new(globals);
+        
+        let result = vm.run(&root);
+        
+        match result {
+            Ok(Value::Int(val)) => assert_eq!(val, 20, "Captured variable should be modified to 20"),
+            Ok(val) => panic!("Expected Int(20), got {:?}", val),
+            Err(e) => panic!("VM Error: {}", e),
         }
     }
 }

src/integration_test.rs

@@ -0,0 +1,91 @@
+#[cfg(test)]
+mod tests {
+    use std::sync::{Arc, Mutex};
+    use crate::ast::parser::Parser;
+    use crate::ast::compiler::binder::Binder;
+    use crate::ast::vm::VM;
+    use crate::ast::types::Value;
+
+    use crate::ast::nodes::UntypedKind;
+
+    #[test]
+    fn test_parse_integer_constant() {
+        let source = "123";
+        let mut parser = Parser::new(source).expect("Failed to create parser");
+        let ast = parser.parse_expression().expect("Failed to parse");
+        
+        if let UntypedKind::Constant(Value::Int(val)) = ast.kind {
+            assert_eq!(val, 123);
+        } else {
+            panic!("Expected Integer constant, got {:?}", ast.kind);
+        }
+    }
+
+    #[test]
+    fn test_parse_negative_integer() {
+        let source = "-42";
+        let mut parser = Parser::new(source).expect("Failed to create parser");
+        let ast = parser.parse_expression().expect("Failed to parse");
+        
+        if let UntypedKind::Constant(Value::Int(val)) = ast.kind {
+            assert_eq!(val, -42);
+        } else {
+            panic!("Expected Integer constant, got {:?}", ast.kind);
+        }
+    }
+
+    #[test]
+    fn test_parse_float_constant() {
+        let source = "123.45";
+        let mut parser = Parser::new(source).expect("Failed to create parser");
+        let ast = parser.parse_expression().expect("Failed to parse");
+        
+        if let UntypedKind::Constant(Value::Float(val)) = ast.kind {
+            assert_eq!(val, 123.45);
+        } else {
+            panic!("Expected Float constant, got {:?}", ast.kind);
+        }
+    }
+
+    #[test]
+    fn test_parse_negative_float() {
+        let source = "-10.5";
+        let mut parser = Parser::new(source).expect("Failed to create parser");
+        let ast = parser.parse_expression().expect("Failed to parse");
+        
+        if let UntypedKind::Constant(Value::Float(val)) = ast.kind {
+            assert_eq!(val, -10.5);
+        } else {
+            panic!("Expected Float constant, got {:?}", ast.kind);
+        }
+    }
+
+    #[test]
+    fn test_closure_modification_from_source() {
+        let source = r#"
+        (do
+            (def x 10)
+            (def f (fn [] (assign x 20)))
+            (f)
+            x
+        )
+        "#;
+
+        let mut parser = Parser::new(source).expect("Failed to create parser");
+        let ast = parser.parse_expression().expect("Failed to parse");
+
+        let globals = Arc::new(Mutex::new(std::collections::HashMap::new()));
+        let mut binder = Binder::new(globals.clone());
+        let bound_ast = binder.bind(&ast).expect("Failed to bind");
+
+        let vm_globals = Arc::new(Mutex::new(Vec::new()));
+        let mut vm = VM::new(vm_globals);
+        let result = vm.run(&bound_ast);
+
+        match result {
+            Ok(Value::Int(val)) => assert_eq!(val, 20, "Closure should modify outer variable"),
+            Ok(val) => panic!("Expected Int(20), got {:?}", val),
+            Err(e) => panic!("VM Error: {}", e),
+        }
+    }
+}

src/main.rs

@@ -2,6 +2,8 @@ use eframe::egui;
 use crate::ast::environment::Environment;
 
 pub mod ast;
+#[cfg(test)]
+mod integration_test;
 
 fn main() -> eframe::Result {
     let options = eframe::NativeOptions {