Implement closures

What a pain.

Next steps: More happy path tests, then large values/mutabilty, then redo in bytecode.

Cargo.toml

@@ -22,3 +22,8 @@ lalrpop = "0.19.6"
 [dev-dependencies]
 assert_cmd = "2.0.2"
 insta = { version = "1.9.0", features = ["glob"] }
+
+[profile.dev]
+# https://github.com/rust-lang/rust/issues/92163
+# https://github.com/rust-lang/rust/issues/92315
+incremental=false

src/ast.rs

@@ -1,20 +1,24 @@
 use std::rc::Rc;
 
-#[derive(Debug, debug2::Debug, PartialEq)]
+#[derive(Debug /*/*, debug2::Debug*/*/, PartialEq)]
 
 crate enum Tree {
     Leaf(Literal),
     Define(String, Box<Tree>),
     If(Box<[Tree; 3]>),
-    Lambda(Lambda),
+    // Its easier to box the lambdas in the parser than the vm, as
+    // here we see all of them exactly once
+    Func(Rc<Func>),
     Branch(Vec<Tree>),
 }
 
-#[derive(Debug, debug2::Debug, PartialEq, Clone)]
+#[derive(Debug /*/*, debug2::Debug*/*/, PartialEq)]
+crate struct Func {
+    crate args: Vec<String>,
+    crate body: Vec<Tree>,
+}
 
-crate struct Lambda(crate Rc<[String]>, crate Rc<[Tree]>);
-
-#[derive(Debug, debug2::Debug, PartialEq)]
+#[derive(Debug /*/*, debug2::Debug*/*/, PartialEq)]
 
 crate enum Literal {
     Sym(String),

src/eval.rs

@@ -1,58 +1,77 @@
 use std::assert_matches::assert_matches;
+use std::cell::RefCell;
 use std::collections::HashMap;
+use std::rc::Rc;
 
 use crate::value::Value;
 use crate::{ast, prims};
 
-pub(crate) fn eval(t: &ast::Tree, env: &mut Env) -> Result<Value, RTError> {
+#[derive(/*debug2::Debug,*/ Debug, Clone)]
+crate struct Lambda {
+    crate func: Rc<ast::Func>,
+    crate captures: Rc<RefCell<Env>>,
+}
+
+pub(crate) fn eval(t: &ast::Tree, env: Rc<RefCell<Env>>) -> Result<Value, RTError> {
     Ok(match t {
         ast::Tree::Leaf(l) => match l {
-            ast::Literal::Sym(s) => match env.lookup(s) {
+            ast::Literal::Sym(s) => match env.borrow().lookup(s) {
                 Some(v) => v,
                 None => return err(format!("Undefined variable `{}`", s)),
             },
             ast::Literal::Num(v) => Value::Num(*v),
             ast::Literal::Bool(b) => Value::Bool(*b),
         },
-        ast::Tree::Lambda(l) => Value::Lambda(l.clone()),
+        ast::Tree::Func(l) => Value::Lambda(Lambda {
+            func: Rc::clone(l),
+            captures: Rc::clone(&env),
+        }),
         ast::Tree::Branch(args) => {
-            let Some(fun) = args.get(0) else { return err("No argument given".to_owned()) };
-            let fun = eval(fun, env)?;
-            let fun = fun.as_func()?;
+            let Some(fun) = args.get(0) else { return err("No func given".to_owned()) };
+
+            let fun = eval(fun, Rc::clone(&env))?.as_func()?;
+
             let args = args
                 .iter()
                 .skip(1)
-                .map(|a| eval(a, env))
+                .map(|a| eval(a, Rc::clone(&env)))
                 .collect::<Result<Vec<_>, _>>()?;
-            // return fun(&args);
+
             match fun {
                 Callable::Func(f) => f(&args)?,
                 Callable::Lambda(l) => {
-                    if l.0.len() == args.len() {
-                        let mut env = env.child();
-                        for (x, y) in l.0.iter().zip(args) {
+                    if l.func.args.len() == args.len() {
+                        // let mut env = env.child();
+                        let mut env = Env::child(Rc::clone(&l.captures));
+
+                        for (x, y) in l.func.args.iter().zip(args) {
                             env.define(x.clone(), y)
                         }
+                        let env = Rc::new(RefCell::new(env));
 
-                        let [main @ .., tail] = &l.1[..] else { unreachable!("Body has 1+ element by parser") };
+                        let [main @ .., tail] = &l.func.body[..] else { unreachable!("Body has 1+ element by parser") };
                         for i in main {
-                            eval(i, &mut env)?;
+                            eval(i, Rc::clone(&env))?;
                         }
 
-                        eval(tail, &mut env)?
+                        eval(tail, env)?
                     } else {
-                        return err(format!("Need {} args, got {}", l.0.len(), args.len()));
+                        return err(format!(
+                            "Need {} args, got {}",
+                            l.func.args.len(),
+                            args.len()
+                        ));
                     }
                 }
             }
         }
         ast::Tree::Define(name, to) => {
-            let val = eval(to, env)?;
-            env.define(name.to_owned(), val);
+            let val = eval(to, Rc::clone(&env))?;
+            env.borrow_mut().define(name.to_owned(), val);
             Value::Trap
         }
         ast::Tree::If(box [cond, tcase, fcase]) => {
-            let b = eval(cond, env)?.as_bool()?;
+            let b = eval(cond, Rc::clone(&env))?.as_bool()?;
             let body = if b { tcase } else { fcase };
             eval(body, env)?
         }
@@ -66,40 +85,60 @@ pub(crate) fn err<T>(s: String) -> Result<T, RTError> {
     Err(RTError(s))
 }
 
-pub(crate) enum Callable<'a> {
-    Func(prims::Func),
-    Lambda(&'a ast::Lambda),
+pub(crate) enum Callable {
+    Func(prims::NativeFunc),
+    Lambda(Lambda),
 }
 
-pub(crate) struct Env<'a> {
-    pub(crate) vars: HashMap<String, Value>,
-    pub(crate) enclosing: Option<&'a Env<'a>>,
+#[derive(Clone /*, debug2::Debug*/)]
+pub(crate) struct Env {
+    vars: HashMap<String, Value>,
+    enclosing: Option<Rc<RefCell<Env>>>,
 }
 
-impl<'a> Env<'a> {
-    pub(crate) fn child(&'a self) -> Env<'a> {
+impl std::fmt::Debug for Env {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        struct Vars<'a>(&'a HashMap<String, Value>);
+
+        impl std::fmt::Debug for Vars<'_> {
+            fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+                f.debug_set().entries(self.0.keys()).finish()
+            }
+        }
+
+        f.debug_struct("Env")
+            .field("vars", &Vars(&self.vars))
+            .field("enclosing", &self.enclosing)
+            .finish()
+    }
+}
+
+impl Env {
+    pub(crate) fn child(this: Rc<RefCell<Self>>) -> Env {
         Env {
             vars: HashMap::new(),
-            enclosing: Some(self),
+            enclosing: Some(this),
         }
     }
 
     pub(crate) fn lookup(&self, s: &str) -> Option<Value> {
         if let Some(v) = self.vars.get(s) {
             Some(v.clone())
-        } else if let Some(parent) = self.enclosing {
-            parent.lookup(s)
+        } else if let Some(parent) = &self.enclosing {
+            parent.borrow().lookup(s)
         } else {
             None
         }
     }
 
     pub(crate) fn define(&mut self, name: String, val: Value) {
+        assert_ne!(val, Value::Trap); // TODO: Better error
+
         self.vars.insert(name, val);
     }
 }
 
-pub(crate) fn default_env() -> Env<'static> {
+pub(crate) fn default_env() -> Env {
     let mut vars = HashMap::new();
 
     for (name, fun) in prims::prims() {

src/grammar.lalrpop

@@ -17,9 +17,10 @@ Trees = Tree+;
 pub(crate) Tree: Tree = {
     "(" <Tree+> ")" => Tree::Branch(<>),
     "(" "define" <Sym> <BTree> ")" => Tree::Define(<>),
-    "(" "define" "(" <name:Sym> <args:RcSlice<Sym>> ")" <body:RcSlice<Tree>> ")" => Tree::Define(name, Box::new(Tree::Lambda(Lambda(args, body)))),
+    "(" "define" "(" <name:Sym> <args:Sym*> ")" <body:Trees> ")" 
+        => Tree::Define(name, Box::new(Tree::Func(Rc::new(Func{args, body})))),
     "(" "if" <Tree> <Tree> <Tree> ")" => Tree::If(Box::new([<>])),
-    "(" "lambda (" <RcSlice<Sym>> ")" <RcSlice<Tree>> ")" => Tree::Lambda(Lambda(<>)),
+    "(" "lambda (" <args:Sym*> ")" <body:Trees> ")" => Tree::Func(Rc::new(Func{<>})),
     Literal => Tree::Leaf(<>),
 }
 

src/main.rs

@@ -4,7 +4,9 @@
 #![feature(crate_visibility_modifier)]
 #![feature(let_else)]
 
+use std::cell::RefCell;
 use std::io;
+use std::rc::Rc;
 
 use rustyline::validate::{
     MatchingBracketValidator, ValidationContext, ValidationResult, Validator,
@@ -33,9 +35,9 @@ fn main() {
 fn run_file(file: &str) -> io::Result<()> {
     let src = std::fs::read_to_string(file)?;
     let tree = grammar::FileParser::new().parse(&src).unwrap();
-    let mut env = eval::default_env();
+    let env = Rc::new(RefCell::new(eval::default_env()));
     for i in tree {
-        eval::eval(&i, &mut env).unwrap();
+        eval::eval(&i, Rc::clone(&env)).unwrap();
     }
     Ok(())
 }
@@ -46,14 +48,23 @@ fn repl() {
         brackets: MatchingBracketValidator::new(),
     }));
 
-    let mut env = eval::default_env();
+    let env = Rc::new(RefCell::new(eval::default_env()));
 
     while let Ok(line) = rl.readline("> ") {
         rl.add_history_entry(&line);
 
         let tree = grammar::TreeParser::new().parse(&line).unwrap();
         // dbg!(&tree);
-        println!("< {:?}", eval::eval(&tree, &mut env))
+        match eval::eval(&tree, Rc::clone(&env)) {
+            Ok(v) => {
+                // Cant use == because it will panic. This is the only
+                // valid comparison to trap
+                if !matches!(v, value::Value::Trap) {
+                    println!("{}", v)
+                }
+            }
+            Err(e) => println!("! {}", e.0),
+        }
     }
 }
 

src/prims.rs

@@ -1,9 +1,12 @@
 use crate::eval::{err, RTError};
 use crate::value::Value;
 
-crate type Func = fn(&[Value]) -> Result<Value, RTError>;
 
-crate fn prims() -> &'static [(&'static str, Func)] {
+type Result = std::result::Result<Value, RTError>;
+
+crate type NativeFunc = for<'a> fn(&'a [Value]) -> Result;
+
+crate fn prims() -> &'static [(&'static str, NativeFunc)] {
     &[
         ("*", mul),
         ("+", add),
@@ -21,25 +24,27 @@ crate fn prims() -> &'static [(&'static str, Func)] {
         (">", gt),
         ("<=", le),
         (">=", ge),
+
+        ("_Z_debug", z_debug)
     ]
 }
 
 // TODO: DRY +-/*
-fn add(args: &[Value]) -> Result<Value, RTError> {
+fn add(args: &[Value]) -> Result {
     args.iter()
         .map(Value::as_num)
         .try_fold(0.0, |a, b| Ok(a + b?))
         .map(Value::Num)
 }
 
-fn mul(args: &[Value]) -> Result<Value, RTError> {
+fn mul(args: &[Value]) -> Result {
     args.iter()
         .map(Value::as_num)
         .try_fold(1.0, |a, b| Ok(a * b?))
         .map(Value::Num)
 }
 
-fn div(args: &[Value]) -> Result<Value, RTError> {
+fn div(args: &[Value]) -> Result {
     let init = args
         .get(0)
         .ok_or_else(|| RTError("`div` needs at least one argument".to_owned()))?
@@ -53,7 +58,7 @@ fn div(args: &[Value]) -> Result<Value, RTError> {
     }))
 }
 
-fn sub(args: &[Value]) -> Result<Value, RTError> {
+fn sub(args: &[Value]) -> Result {
     let init = args
         .get(0)
         .ok_or_else(|| RTError("`sub` needs at least one argument".to_owned()))?
@@ -67,17 +72,17 @@ fn sub(args: &[Value]) -> Result<Value, RTError> {
     }))
 }
 
-fn equals(args: &[Value]) -> Result<Value, RTError> {
+fn equals(args: &[Value]) -> Result {
     Ok(Value::Bool(args.array_windows().all(|[l, r]| l == r)))
 }
 
-fn display(args: &[Value]) -> Result<Value, RTError> {
+fn display(args: &[Value]) -> Result {
     let [arg] = args else {return err("To many args to `display`".to_owned())};
-    print!("{:?}", arg);
+    print!("{}", arg);
     Ok(Value::Trap)
 }
 
-fn newline(args: &[Value]) -> Result<Value, RTError> {
+fn newline(args: &[Value]) -> Result {
     if !args.is_empty() {
         return err("Newline takes no args".to_owned());
     }
@@ -85,7 +90,7 @@ fn newline(args: &[Value]) -> Result<Value, RTError> {
     Ok(Value::Trap)
 }
 
-fn abs(args: &[Value]) -> Result<Value, RTError> {
+fn abs(args: &[Value]) -> Result {
     let [v] = args else { return err("abs takes 1 arg".to_owned()) };
     let ans = v.as_num()?.abs();
     Ok(Value::Num(ans))
@@ -95,7 +100,7 @@ crate fn compare_core(
     args: &[Value],
     f: fn(f64, f64) -> bool,
     name: &'static str,
-) -> Result<Value, RTError> {
+) -> Result {
     for [l, r] in args.array_windows() {
         let (Value::Num(l), Value::Num(r)) = (l,r) else 
         { 
@@ -114,11 +119,16 @@ crate fn compare_core(
 macro_rules! cmps {
     ($(($name:ident $op:tt))*) => {
         $(
-            fn $name(args: &[Value]) -> Result<Value, RTError> {
+            fn $name(args: &[Value]) -> Result {
                 compare_core(args, |l, r| l $op r, stringify!($op))
             }
         )*
     };
 }
 
-cmps! { (lt <) (gt >) (le <=) (ge >=) }
+cmps! { (lt <) (gt >) (le <=) (ge >=) }
+
+fn z_debug(args: &[Value]) -> Result {
+    eprintln!("{:?}", args);
+    Ok(Value::Trap)
+}

src/snapshots/handball__tests__run-pass@ambig-scope.scm.snap

@@ -0,0 +1,13 @@
+---
+source: src/tests.rs
+assertion_line: 41
+expression: run-pass ambig-scope.scm
+
+---
+
+42.0
+1.0
+2.0
+3.0
+2.0
+1.0

src/snapshots/handball__tests__run-pass@capture.scm.snap

@@ -0,0 +1,9 @@
+---
+source: src/tests.rs
+assertion_line: 41
+expression: run-pass capture.scm
+
+---
+#<procedure>
+2.0
+

src/snapshots/handball__tests__run-pass@curry.scm.snap

@@ -0,0 +1,8 @@
+---
+source: src/tests.rs
+assertion_line: 41
+expression: run-pass curry.scm
+
+---
+3.0
+

src/test/run-pass/ambig-scope.scm

@@ -0,0 +1,18 @@
+#lang scheme
+
+(define (displayln x) (newline) (display x))
+
+(define (ambig1 x) (lambda (x) x))
+
+(displayln ((ambig1 13) 42))
+
+(define (ambig2 a)
+  (displayln a)
+  (define a- a)
+  (lambda (b) (displayln b)
+    (lambda (a)
+      (displayln a)
+      (displayln b)
+      (displayln a-))))
+
+(((ambig2 1) 2) 3)

src/test/run-pass/capture.scm

@@ -0,0 +1,12 @@
+#lang scheme
+
+(define (displayln x) (display x) (newline))
+
+
+(define (const x) (lambda () x))
+
+(define two-thunk (const 2))
+
+(displayln two-thunk)
+(displayln (two-thunk))
+

src/test/run-pass/curry.scm

@@ -0,0 +1,7 @@
+#lang scheme
+
+(define (displayln x) (display x) (newline))
+
+(define (curry2 f) (lambda (l) (lambda (r) (f l r))))
+
+(displayln (((curry2 +) 1) 2))

src/value.rs

@@ -1,16 +1,32 @@
-use crate::{ast, eval, prims};
+use crate::{eval, prims};
 use std::rc::Rc;
 
-#[derive(Clone)]
+#[derive(Clone /*, debug2::Debug*/)]
 crate enum Value {
     Num(f64),
-    Func(prims::Func),
-    Lambda(ast::Lambda),
+    // TODO: implement debug2::Debug for `fn` type, and do it right
+    // https://godbolt.org/z/vr9erGeKq
+    Func(prims::NativeFunc),
+    Lambda(eval::Lambda),
     Bool(bool),
     /// Result of things that shouldnt have values, like (define x 3)
+    /// TODO: Figure this out
     Trap,
 }
 
+impl std::fmt::Debug for Value {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Num(arg0) => f.debug_tuple("Num").field(arg0).finish(),
+            // We cant just pass the field because of livetime bs, see https://godbolt.org/z/vr9erGeKq
+            Self::Func(_) => f.debug_struct("Func").finish_non_exhaustive(),
+            Self::Lambda(arg0) => f.debug_tuple("Lambda").field(arg0).finish(),
+            Self::Bool(arg0) => f.debug_tuple("Bool").field(arg0).finish(),
+            Self::Trap => write!(f, "Trap"),
+        }
+    }
+}
+
 impl PartialEq for Value {
     fn eq(&self, other: &Self) -> bool {
         use Value::*;
@@ -18,7 +34,9 @@ impl PartialEq for Value {
             (Num(l), Num(r)) => l == r,
             (Func(l), Func(r)) => *l as usize == *r as usize,
             (Bool(l), Bool(r)) => l == r,
-            (Lambda(l), Lambda(r)) => Rc::ptr_eq(&l.0, &r.0) && Rc::ptr_eq(&l.1, &r.1),
+            (Lambda(l), Lambda(r)) => {
+                Rc::ptr_eq(&l.func, &r.func) && Rc::ptr_eq(&l.captures, &r.captures)
+            }
 
             (Num(_), _) => false,
             (Func(_), _) => false,
@@ -30,10 +48,10 @@ impl PartialEq for Value {
     }
 }
 
-impl std::fmt::Debug for Value {
+impl std::fmt::Display for Value {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         match self {
-            Self::Num(n) => n.fmt(f),
+            Self::Num(n) => std::fmt::Debug::fmt(n, f), // TODO: Change to displays
             Self::Func(_) => f.write_str("#<procedure>"),
             Self::Lambda(_) => f.write_str("#<procedure>"),
             Self::Bool(b) => f.write_str(if *b { "#t" } else { "#f" }),
@@ -51,14 +69,11 @@ impl Value {
         }
     }
 
-    crate fn as_func(&self) -> Result<eval::Callable, eval::RTError> {
+    crate fn as_func(self) -> Result<eval::Callable, eval::RTError> {
         match self {
-            Self::Func(f) => Ok(eval::Callable::Func(*f)),
+            Self::Func(f) => Ok(eval::Callable::Func(f)),
             Self::Lambda(l) => Ok(eval::Callable::Lambda(l)),
-            _ => Err(eval::RTError(format!(
-                "Expected a function, got {:?}",
-                self
-            ))),
+            _ => Err(eval::RTError(format!("Expected a function, got {}", self))),
         }
     }