Add AST dumper and improve upvalue analysis

The `UpvalueAnalyzer` now correctly identifies which lambdas capture
which variable declarations, rather than just marking declarations that
need boxing. This information is stored in a `capture_map`.

The `Binder` has been updated to use this new `capture_map` instead of a
`HashSet` of boxed declarations. The `DefLocal` node in `bound_nodes.rs`
now stores a `captured_by` field, which is a list of lambda identities
that capture the local variable.

A new `dumper` module has been added to provide a human-readable
representation of the bound AST, including information about captured
variables.

The `VM` has been updated to use the `captured_by` field to determine if
a local variable needs to be stored in a `Cell`, rather than relying on
a boolean `is_boxed` flag.

An example script `extreme_capture.myc` has been added to test deep
nesting and variable capture.

A new "Dump AST" button has been added to the UI, which uses the new
`Dumper` to display the bound AST.

examples/extreme_capture.myc

@@ -0,0 +1,25 @@
+;; Output: 36
+(do
+  ;; Excessive capture test
+  ;; This script creates deep nesting where the inner-most lambda
+  ;; grabs variables from every single outer scope.
+
+  (def excessive (fn [v1]
+    (do
+      (def v2 2)
+      (fn [v3]
+        (do
+          (def v4 4)
+          (fn [v5]
+            (do
+              (def v6 6)
+              (fn [v7]
+                (do
+                  (def v8 8)
+                  ;; v1, v3, v5, v7 are parameters (captured as upvalues)
+                  ;; v2, v4, v6, v8 are locals (captured from outer scopes)
+                  (+ v1 v2 v3 v4 v5 v6 v7 v8))))))))))
+
+  ;; Execution: (1 + 2 + 3 + 4 + 5 + 6 + 7 + 8) = 36
+  ((((excessive 1) 3) 5) 7)
+)

src/ast/compiler/binder.rs

@@ -1,4 +1,4 @@
-use std::collections::{HashMap, BTreeMap, HashSet};
+use std::collections::{HashMap, BTreeMap};
 use std::rc::Rc;
 use std::cell::RefCell;
 use crate::ast::nodes::{Node, UntypedKind};
@@ -64,28 +64,28 @@ pub struct Binder {
     functions: Vec<FunctionCompiler>,
     // Globals mapping: Name -> (Index, Type)
     globals: Rc<RefCell<HashMap<String, (u32, StaticType)>>>,
-    // Identities of definitions that need boxing (pre-calculated)
-    boxed_declarations: HashSet<Identity>,
+    // Map of Declaration Identity -> List of Lambda Identities that capture it
+    capture_map: HashMap<Identity, Vec<Identity>>,
 }
 
 impl Binder {
     pub fn new(globals: Rc<RefCell<HashMap<String, (u32, StaticType)>>>) -> Self {
-        Self::with_boxed(globals, HashSet::new())
+        Self::with_boxed(globals, HashMap::new())
     }
 
-    fn with_boxed(globals: Rc<RefCell<HashMap<String, (u32, StaticType)>>>, boxed: HashSet<Identity>) -> Self {
+    fn with_boxed(globals: Rc<RefCell<HashMap<String, (u32, StaticType)>>>, captures: HashMap<Identity, Vec<Identity>>) -> Self {
         let mut binder = Self {
             functions: Vec::new(),
             globals,
-            boxed_declarations: boxed,
+            capture_map: captures,
         };
         binder.functions.push(FunctionCompiler::new());
         binder
     }
 
     pub fn bind_root(globals: Rc<RefCell<HashMap<String, (u32, StaticType)>>>, node: &Node<UntypedKind>) -> Result<Node<BoundKind, StaticType>, String> {
-        let boxed = crate::ast::compiler::upvalues::UpvalueAnalyzer::analyze(node);
-        let mut binder = Self::with_boxed(globals, boxed);
+        let captures = crate::ast::compiler::upvalues::UpvalueAnalyzer::analyze(node);
+        let mut binder = Self::with_boxed(globals, captures);
         binder.bind(node)
     }
 
@@ -170,11 +170,11 @@ impl Binder {
                             info.ty = ty.clone();
                         }
                     }
-                    let is_boxed = self.boxed_declarations.contains(&node.identity);
+                    let captured_by = self.capture_map.get(&node.identity).cloned().unwrap_or_default();
                     Ok(self.make_node(node.identity.clone(), BoundKind::DefLocal { 
                         slot: slot_or_idx, 
                         value: Box::new(val_node) ,
-                        is_boxed
+                        captured_by
                     }, ty))
                 }
             },
@@ -361,8 +361,8 @@ mod tests {
         if let BoundKind::Lambda { body, .. } = &bound.kind {
             if let BoundKind::Block { exprs } = &body.kind {
                 let x_decl = &exprs[0];
-                if let BoundKind::DefLocal { is_boxed, .. } = &x_decl.kind {
-                    assert!(is_boxed, "Variable 'x' should be marked as boxed because it is captured by lambda 'f'");
+                if let BoundKind::DefLocal { captured_by, .. } = &x_decl.kind {
+                    assert!(!captured_by.is_empty(), "Variable 'x' should have capturers because it is used in lambda 'f'");
                 } else {
                     panic!("First expression in block should be DefLocal, got {:?}", x_decl.kind);
                 }
@@ -386,8 +386,8 @@ mod tests {
         if let BoundKind::Lambda { body, .. } = &bound.kind {
             if let BoundKind::Block { exprs } = &body.kind {
                 let x_decl = &exprs[0];
-                if let BoundKind::DefLocal { is_boxed, .. } = &x_decl.kind {
-                    assert!(!is_boxed, "Variable 'x' should NOT be boxed as it is not captured");
+                if let BoundKind::DefLocal { captured_by, .. } = &x_decl.kind {
+                    assert!(captured_by.is_empty(), "Variable 'x' should NOT have any capturers");
                 } else {
                     panic!("First expression should be DefLocal");
                 }

src/ast/compiler/bound_nodes.rs

@@ -1,5 +1,5 @@
 use std::rc::Rc;
-use crate::ast::types::{Value, StaticType};
+use crate::ast::types::{Value, StaticType, Identity};
 use crate::ast::nodes::Node;
 
 #[derive(Debug, Clone, Copy, PartialEq)]
@@ -27,7 +27,7 @@ pub enum BoundKind {
     DefLocal {
         slot: u32,
         value: Box<Node<BoundKind, StaticType>>,
-        is_boxed: bool,
+        captured_by: Vec<Identity>,
     },
 
     If {

src/ast/compiler/dumper.rs

@@ -0,0 +1,154 @@
+use crate::ast::nodes::Node;
+use crate::ast::compiler::bound_nodes::BoundKind;
+use crate::ast::types::StaticType;
+
+/// Human-readable AST dumper for the bound AST.
+pub struct Dumper {
+    output: String,
+    indent: usize,
+}
+
+impl Dumper {
+    /// Produces a formatted string representation of the given bound AST node and its children.
+    pub fn dump(node: &Node<BoundKind, StaticType>) -> String {
+        let mut dumper = Self {
+            output: String::new(),
+            indent: 0,
+        };
+        dumper.visit(node);
+        dumper.output
+    }
+
+    fn write_indent(&mut self) {
+        for _ in 0..self.indent {
+            self.output.push_str("  ");
+        }
+    }
+
+    fn log(&mut self, label: &str, node: &Node<BoundKind, StaticType>) {
+        self.write_indent();
+        self.output.push_str(label);
+        self.output.push_str(&format!(" <Type: {:?}>\n", node.ty));
+    }
+
+    fn visit(&mut self, node: &Node<BoundKind, StaticType>) {
+        match &node.kind {
+            BoundKind::Nop => self.log("Nop", node),
+            BoundKind::Constant(v) => self.log(&format!("Constant: {}", v), node),
+            BoundKind::Get(addr) => self.log(&format!("Get: {:?}", addr), node),
+            
+            BoundKind::Set { addr, value } => {
+                self.log(&format!("Set: {:?}", addr), node);
+                self.indent += 1;
+                self.visit(value);
+                self.indent -= 1;
+            }
+
+            BoundKind::DefLocal { slot, value, captured_by } => {
+                let capture_info = if captured_by.is_empty() {
+                    String::from("not captured")
+                } else {
+                    format!("captured by {} lambdas", captured_by.len())
+                };
+                self.log(&format!("DefLocal (Slot: {}, {})", slot, capture_info), node);
+                
+                self.indent += 1;
+                if !captured_by.is_empty() {
+                    for capturer in captured_by {
+                        self.write_indent();
+                        self.output.push_str(&format!("- Capturer: Lambda at line {}, col {}\n", 
+                            capturer.location.line, capturer.location.col));
+                    }
+                }
+                self.visit(value);
+                self.indent -= 1;
+            }
+
+            BoundKind::DefGlobal { global_index, value } => {
+                self.log(&format!("DefGlobal (Index: {})", global_index), node);
+                self.indent += 1;
+                self.visit(value);
+                self.indent -= 1;
+            }
+
+            BoundKind::If { cond, then_br, else_br } => {
+                self.log("If", node);
+                self.indent += 1;
+                
+                self.write_indent();
+                self.output.push_str("Condition:\n");
+                self.visit(cond);
+                
+                self.write_indent();
+                self.output.push_str("Then:\n");
+                self.visit(then_br);
+                
+                if let Some(e) = else_br {
+                    self.write_indent();
+                    self.output.push_str("Else:\n");
+                    self.visit(e);
+                }
+                self.indent -= 1;
+            }
+
+            BoundKind::Lambda { param_count, upvalues, body } => {
+                self.log(&format!("Lambda (Params: {}, Upvalues: {})", param_count, upvalues.len()), node);
+                self.indent += 1;
+                if !upvalues.is_empty() {
+                    self.write_indent();
+                    self.output.push_str(&format!("Upvalues: {:?}\n", upvalues));
+                }
+                self.visit(body);
+                self.indent -= 1;
+            }
+
+            BoundKind::Call { callee, args } => {
+                self.log("Call", node);
+                self.indent += 1;
+                self.visit(callee);
+                for arg in args {
+                    self.visit(arg);
+                }
+                self.indent -= 1;
+            }
+            
+            BoundKind::TailCall { callee, args } => {
+                self.log("TailCall (TCO)", node);
+                self.indent += 1;
+                self.visit(callee);
+                for arg in args {
+                    self.visit(arg);
+                }
+                self.indent -= 1;
+            }
+
+            BoundKind::Block { exprs } => {
+                self.log("Block", node);
+                self.indent += 1;
+                for expr in exprs {
+                    self.visit(expr);
+                }
+                self.indent -= 1;
+            }
+
+            BoundKind::Tuple { elements } => {
+                self.log("Tuple", node);
+                self.indent += 1;
+                for el in elements {
+                    self.visit(el);
+                }
+                self.indent -= 1;
+            }
+
+            BoundKind::Map { entries } => {
+                self.log("Map", node);
+                self.indent += 1;
+                for (k, v) in entries {
+                    self.visit(k);
+                    self.visit(v);
+                }
+                self.indent -= 1;
+            }
+        }
+    }
+}

src/ast/compiler/mod.rs

@@ -2,8 +2,10 @@ pub mod binder;
 pub mod bound_nodes;
 pub mod tco;
 pub mod upvalues;
+pub mod dumper;
 
 pub use binder::*;
 pub use bound_nodes::*;
 pub use tco::*;
 pub use upvalues::*;
+pub use dumper::*;

src/ast/compiler/tco.rs

@@ -98,9 +98,9 @@ impl TCO {
                     ..node
                 }
             },
-            BoundKind::DefLocal { slot, value, is_boxed } => {
+            BoundKind::DefLocal { slot, value, captured_by } => {
                  Node {
-                    kind: BoundKind::DefLocal { slot, value: Box::new(Self::transform(*value, false)), is_boxed },
+                    kind: BoundKind::DefLocal { slot, value: Box::new(Self::transform(*value, false)), captured_by },
                     ..node
                 }
             },

src/ast/compiler/upvalues.rs

@@ -3,85 +3,94 @@ use std::rc::Rc;
 use crate::ast::nodes::{Node, UntypedKind};
 use crate::ast::types::Identity;
 
-/// Analyzes the AST to find all variable declarations that are captured by nested lambdas.
-/// Returns a set of Identities corresponding to the 'Def' nodes that need boxing.
+/// Analyzes the AST to find which lambdas capture which variable declarations.
+/// Returns a map: Declaration Identity -> List of Lambda Identities that capture it.
 pub struct UpvalueAnalyzer;
 
 impl UpvalueAnalyzer {
-    pub fn analyze(root: &Node<UntypedKind>) -> HashSet<Identity> {
-        let mut boxed = HashSet::new();
+    pub fn analyze(root: &Node<UntypedKind>) -> HashMap<Identity, Vec<Identity>> {
+        let mut capture_map: HashMap<Identity, HashSet<Identity>> = HashMap::new();
         let mut scopes = vec![HashMap::new()]; // Root scope
-        Self::visit(root, &mut scopes, &mut boxed);
-        boxed
+        
+        Self::visit(root, &mut scopes, &mut capture_map, None);
+        
+        // Convert HashSet back to sorted Vec for the final result
+        capture_map.into_iter()
+            .map(|(decl, lambdas)| (decl, lambdas.into_iter().collect()))
+            .collect()
     }
 
-    fn visit(node: &Node<UntypedKind>, scopes: &mut Vec<HashMap<Rc<str>, Identity>>, boxed: &mut HashSet<Identity>) {
+    fn visit(
+        node: &Node<UntypedKind>, 
+        scopes: &mut Vec<HashMap<Rc<str>, Identity>>, 
+        capture_map: &mut HashMap<Identity, HashSet<Identity>>,
+        current_lambda: Option<Identity>
+    ) {
         match &node.kind {
             UntypedKind::Identifier(name) => {
                 // Resolve name in scope stack (from inner to outer)
                 for (depth, scope) in scopes.iter().rev().enumerate() {
-                    if let Some(id) = scope.get(name) {
+                    if let Some(decl_id) = scope.get(name) {
                         if depth > 0 {
                             // Captured from an outer scope!
-                            boxed.insert(id.clone());
+                            if let Some(lambda_id) = &current_lambda {
+                                capture_map.entry(decl_id.clone())
+                                    .or_insert_with(HashSet::new)
+                                    .insert(lambda_id.clone());
+                            }
                         }
                         break;
                     }
                 }
             }
             UntypedKind::Def { name, value } => {
-                // 1. Visit initializer first (it executes in current scope)
-                Self::visit(value, scopes, boxed);
-                
-                // 2. Define the variable in current scope
+                Self::visit(value, scopes, capture_map, current_lambda.clone());
                 if let Some(current) = scopes.last_mut() {
                     current.insert(name.clone(), node.identity.clone());
                 }
             }
             UntypedKind::Lambda { params, body } => {
-                // Enter new lambda scope
                 let mut new_scope = HashMap::new();
                 for p in params {
-                    // Parameters are defined in the new scope, masking outer ones.
-                    // We use the lambda's identity as a placeholder for parameter origin.
                     new_scope.insert(p.clone(), node.identity.clone());
                 }
                 
                 scopes.push(new_scope);
-                Self::visit(body, scopes, boxed);
+                // The current node is the lambda causing captures in its body
+                Self::visit(body, scopes, capture_map, Some(node.identity.clone()));
                 scopes.pop();
             }
             UntypedKind::If { cond, then_br, else_br } => {
-                Self::visit(cond, scopes, boxed);
-                Self::visit(then_br, scopes, boxed);
+                Self::visit(cond, scopes, capture_map, current_lambda.clone());
+                Self::visit(then_br, scopes, capture_map, current_lambda.clone());
                 if let Some(e) = else_br {
-                    Self::visit(e, scopes, boxed);
+                    Self::visit(e, scopes, capture_map, current_lambda.clone());
                 }
             }
             UntypedKind::Assign { target, value } => {
-                Self::visit(target, scopes, boxed);
-                Self::visit(value, scopes, boxed);
+                Self::visit(target, scopes, capture_map, current_lambda.clone());
+                Self::visit(value, scopes, capture_map, current_lambda.clone());
             }
             UntypedKind::Call { callee, args } => {
-                Self::visit(callee, scopes, boxed);
+                Self::visit(callee, scopes, capture_map, current_lambda.clone());
                 for arg in args {
-                    Self::visit(arg, scopes, boxed);
+                    Self::visit(arg, scopes, capture_map, current_lambda.clone());
                 }
             }
             UntypedKind::Block { exprs } => {
                 for expr in exprs {
-                    Self::visit(expr, scopes, boxed);
+                    Self::visit(expr, scopes, capture_map, current_lambda.clone());
                 }
             }
             UntypedKind::Tuple { elements } => {
                 for el in elements {
-                    Self::visit(el, scopes, boxed);
+                    Self::visit(el, scopes, capture_map, current_lambda.clone());
                 }
             }
             UntypedKind::Map { entries } => {
                 for (k, v) in entries {
-                    Self::visit(k, scopes, boxed);
-                    Self::visit(v, scopes, boxed);
+                    Self::visit(k, scopes, capture_map, current_lambda.clone());
+                    Self::visit(v, scopes, capture_map, current_lambda.clone());
                 }
             }
             UntypedKind::Nop | UntypedKind::Constant(_) | UntypedKind::Extension(_) => {}

src/ast/environment.rs

@@ -8,6 +8,8 @@ use crate::ast::vm::VM;
 
 use crate::ast::compiler::tco::TCO;
 
+use crate::ast::compiler::dumper::Dumper;
+
 pub struct Environment {
     pub global_names: Rc<RefCell<HashMap<String, (u32, StaticType)>>>,
     pub global_values: Rc<RefCell<Vec<Value>>>,
@@ -105,6 +107,16 @@ impl Environment {
         });
     }
 
+    pub fn dump_ast(&self, source: &str) -> Result<String, String> {
+        let mut parser = Parser::new(source)?;
+        let untyped_ast = parser.parse_expression()?;
+        
+        let bound_ast = Binder::bind_root(self.global_names.clone(), &untyped_ast)?;
+        let optimized_ast = TCO::optimize(bound_ast);
+        
+        Ok(Dumper::dump(&optimized_ast))
+    }
+
     pub fn run_script(&self, source: &str) -> Result<Value, String> {
         // 1. Parse
         let mut parser = Parser::new(source)?;

src/ast/vm.rs

@@ -82,9 +82,9 @@ impl VM {
                 Ok(val)
             },
 
-            BoundKind::DefLocal { slot, value, is_boxed } => {
+            BoundKind::DefLocal { slot, value, captured_by } => {
                 let val = self.eval(value)?;
-                let final_val = if *is_boxed {
+                let final_val = if !captured_by.is_empty() {
                     Value::Cell(Rc::new(RefCell::new(val)))
                 } else {
                     val

src/main.rs

@@ -85,7 +85,21 @@ impl CompilerApp {
                 );
             }
             Err(e) => {
-                self.output_log = format!("Error: {}", e);
+                self.output_log = format!("Error during Compilation/Execution: {}", e);
+            }
+        }
+    }
+
+    fn dump_ast(&mut self) {
+        match self.env.dump_ast(&self.source_code) {
+            Ok(dump) => {
+                self.output_log = format!(
+                    "--- BOUND AST DUMP ---\n\n{}",
+                    dump
+                );
+            }
+            Err(e) => {
+                self.output_log = format!("Error during AST Binding: {}", e);
             }
         }
     }
@@ -213,6 +227,10 @@ impl eframe::App for CompilerApp {
                         self.compile();
                     }
 
+                    if ui.button("Dump AST").clicked() {
+                        self.dump_ast();
+                    }
+
                     if let Some(path) = &self.current_example_path {
                         let file_name = path.file_name().unwrap_or_default().to_string_lossy();
                         if ui.button(format!("Save {} (Ctrl+S)", file_name)).clicked() {