a slow and brute-force approach to the problem of re-binding closed-over forward declarations

src/base.rs

@@ -50,8 +50,8 @@ pub fn store<'src>(b: &Value<'src>, val: &Value<'src>) -> Value<'src> {
 pub fn doc<'src>(f: &Value<'src>) -> Value<'src> {
     match f {
         Value::Fn(f) => {
-            let name = &f.name;
+            let name = &f.borrow().name;
-            let doc = &f.doc;
+            let doc = &f.borrow().doc;
             if let Some(docstr) = doc {
                 Value::AllocatedString(Rc::new(format!("{name}: {docstr}")))
             } else {
@@ -384,6 +384,7 @@ pub fn r#type<'src>(x: &Value<'src>) -> Value<'src> {
         Value::Args(_) => unreachable!("internal Ludus error"),
         Value::Base(_) => Value::Keyword("fn"),
         Value::Recur(..) => unreachable!("internal Ludus error"),
+        Value::FnDecl(_) => Value::Keyword("fn"),
     }
 }
 

src/main.rs

@@ -59,6 +59,9 @@ use crate::validator::*;
 mod process;
 use crate::process::*;
 
+mod errors;
+use crate::errors::*;
+
 #[derive(Embed)]
 #[folder = "assets/"]
 struct Asset;
@@ -176,17 +179,22 @@ pub fn run(src: &'static str) {
 
     match result {
         Ok(result) => println!("{}", result),
-        Err(LErr { msg, .. }) => println!("Ludus panicked!\n{}", msg),
+        Err(err) => report_panic(err, src),
     }
 }
 
 pub fn main() {
     let src = "
-let guard = :nil
+fn bar
-match :foo with {
+fn foo () -> {:foo}
-    :foo if guard -> :guarded
+
-    _ -> :unguarded
+let quux = foo
-}
+let fuzz = :asdf
+
+fn baz (...) -> bar ()
+
+fn bar () -> quux ()
+baz (1, 2, 3)
     ";
     run(src);
     // struct_scalpel::print_dissection_info::<value::Value>()

src/process.rs

@@ -10,26 +10,23 @@ use std::cell::RefCell;
 use std::rc::Rc;
 
 #[derive(Debug)]
-pub struct LErr {
+pub struct LErr<'src> {
     pub msg: String,
-    pub trace: Vec<String>,
+    pub span: SimpleSpan,
+    pub trace: Vec<(Spanned<Ast>, Spanned<Ast>, Value<'src>, Value<'src>)>,
 }
 
-impl LErr {
+impl<'src> LErr<'src> {
-    pub fn new(msg: String) -> LErr {
+    pub fn new(msg: String, span: SimpleSpan) -> LErr<'src> {
         LErr {
-            msg: msg.to_string(),
+            msg,
+            span,
             trace: vec![],
         }
     }
-
-    pub fn add_trace(mut self, fn_name: String) -> LErr {
-        self.trace.push(fn_name);
-        self
-    }
 }
 
-type LResult<'src> = Result<Value<'src>, LErr>;
+type LResult<'src> = Result<Value<'src>, LErr<'src>>;
 
 #[derive(Debug)]
 pub struct Process<'src> {
@@ -50,12 +47,16 @@ impl<'src> Process<'src> {
                 let resolved_prelude = self.prelude.iter().rev().find(|(name, _)| word == name);
                 match resolved_prelude {
                     Some((_, value)) => Ok(value.clone()),
-                    None => Err(LErr::new(format!("unbound name {word}"))),
+                    None => Err(LErr::new(format!("unbound name `{word}`"), self.span)),
                 }
             }
         }
     }
 
+    pub fn panic(&self, msg: String) -> LResult<'src> {
+        Err(LErr::new(msg, self.span))
+    }
+
     pub fn bind(&mut self, word: String, value: &Value<'src>) {
         self.locals.push((word, value.clone()));
     }
@@ -223,7 +224,7 @@ impl<'src> Process<'src> {
                     return result;
                 }
             }
-            Err(LErr::new("no match".to_string()))
+            self.panic("no match".to_string())
         }
     }
 
@@ -245,8 +246,26 @@ impl<'src> Process<'src> {
                 }
             }
             (Fn(f), Tuple(args)) => {
+                // can't just use the `caller` value b/c borrow checker nonsense
                 let args = Tuple(args);
                 let to = self.locals.len();
+                let mut f = f.borrow_mut();
+                for i in 0..f.enclosing.len() {
+                    let (name, value) = f.enclosing[i].clone();
+                    if matches!(value, Value::FnDecl(_)) {
+                        let defined = self.resolve(&name);
+                        match defined {
+                            Ok(Value::Fn(defined)) => f.enclosing[i] = (name.clone(), Fn(defined)),
+                            Ok(Value::FnDecl(_)) => {
+                                return self.panic(format!(
+                                    "function `{name}` called before it was defined"
+                                ))
+                            }
+
+                            _ => unreachable!("internal Ludus error"),
+                        }
+                    }
+                }
                 let mut enclosing = f.enclosing.clone();
                 self.locals.append(&mut enclosing);
                 let result = self.match_clauses(&args, f.body);
@@ -256,14 +275,15 @@ impl<'src> Process<'src> {
             // TODO: partially applied functions shnould work! In #15
             (Fn(_f), Args(_args)) => todo!(),
             (_, Keyword(_)) => Ok(Nil),
-            (_, Args(_)) => Err(LErr::new("you may only call a function".to_string())),
+            (_, Args(_)) => Err(LErr::new(
+                "you may only call a function".to_string(),
+                self.span,
+            )),
             (Base(f), Tuple(args)) => match f {
                 BaseFn::Nullary(f) => {
                     let num_args = args.len();
                     if num_args != 0 {
-                        Err(LErr::new(format!(
+                        self.panic(format!("wrong arity: expected 0 arguments, got {num_args}"))
-                            "wrong arity: expected 0 arguments, got {num_args}"
-                        )))
                     } else {
                         Ok(f())
                     }
@@ -271,9 +291,7 @@ impl<'src> Process<'src> {
                 BaseFn::Unary(f) => {
                     let num_args = args.len();
                     if num_args != 1 {
-                        Err(LErr::new(format!(
+                        self.panic(format!("wrong arity: expected 1 argument, got {num_args}"))
-                            "wrong arity: expected 1 argument, got {num_args}"
-                        )))
                     } else {
                         Ok(f(&args[0]))
                     }
@@ -281,9 +299,7 @@ impl<'src> Process<'src> {
                 BaseFn::Binary(r#fn) => {
                     let num_args = args.len();
                     if num_args != 2 {
-                        Err(LErr::new(format!(
+                        self.panic(format!("wrong arity: expected 2 arguments, got {num_args}"))
-                            "wrong arity: expected 2 arguments, got {num_args}"
-                        )))
                     } else {
                         Ok(r#fn(&args[0], &args[1]))
                     }
@@ -291,9 +307,7 @@ impl<'src> Process<'src> {
                 BaseFn::Ternary(f) => {
                     let num_args = args.len();
                     if num_args != 3 {
-                        Err(LErr::new(format!(
+                        self.panic(format!("wrong arity: expected 3 arguments, got {num_args}"))
-                            "wrong arity: expected 3 arguments, got {num_args}"
-                        )))
                     } else {
                         Ok(f(&args[0], &args[1], &args[2]))
                     }
@@ -355,9 +369,8 @@ impl<'src> Process<'src> {
                         Ast::Splat(_) => match member_value {
                             Value::List(list) => vect.append(list),
                             _ => {
-                                return Err(LErr::new(
+                                return self
-                                    "only lists may be splatted into lists".to_string(),
+                                    .panic("only lists may be splatted into lists".to_string())
-                                ))
                             }
                         },
                         _ => vect.push_back(member_value),
@@ -380,7 +393,7 @@ impl<'src> Process<'src> {
                 let val = self.visit(expr)?;
                 let result = match self.match_pattern(&patt.0, &val) {
                     Some(_) => Ok(val),
-                    None => Err(LErr::new("no match".to_string())),
+                    None => self.panic("no match".to_string()),
                 };
                 result
             }
@@ -407,9 +420,7 @@ impl<'src> Process<'src> {
                         (Ast::Splat(_), _) => {
                             let resolved = self.visit(term)?;
                             let Value::Dict(to_splat) = resolved else {
-                                return Err(LErr::new(
+                                return self.panic("cannot splat non-dict into dict".to_string());
-                                    "cannot splat non-dict into dict".to_string(),
-                                ));
                             };
                             dict = to_splat.union(dict);
                         }
@@ -427,12 +438,28 @@ impl<'src> Process<'src> {
             Synthetic(root, first, rest) => {
                 let root_val = self.visit(root)?;
                 let first_val = self.visit(first)?;
-                let mut curr = self.apply(root_val, first_val)?;
+                let mut result = self.apply(root_val.clone(), first_val.clone());
+                if let Err(mut err) = result {
+                    err.trace
+                        .push((*root.clone(), *first.clone(), root_val, first_val));
+                    return Err(err);
+                };
+                let mut prev_node;
+                let mut this_node = first.as_ref();
                 for term in rest.iter() {
-                    let next = self.visit(term)?;
+                    prev_node = this_node;
-                    curr = self.apply(curr, next)?;
+                    this_node = term;
+                    let caller = self.visit(term)?;
+                    let callee = result.unwrap();
+                    result = self.apply(callee.clone(), caller.clone());
+
+                    if let Err(mut err) = result {
+                        err.trace
+                            .push((prev_node.clone(), this_node.clone(), caller, callee));
+                        return Err(err);
                     }
-                Ok(curr)
+                }
+                result
             }
             When(clauses) => {
                 for clause in clauses.iter() {
@@ -443,7 +470,7 @@ impl<'src> Process<'src> {
                         return self.visit(body);
                     };
                 }
-                Err(LErr::new("no match".to_string()))
+                self.panic("no match".to_string())
             }
             Match(scrutinee, clauses) => {
                 let value = self.visit(scrutinee)?;
@@ -461,24 +488,43 @@ impl<'src> Process<'src> {
                     .filter(|binding| binding != name)
                     .map(|binding| (binding.clone(), self.resolve(binding).unwrap().clone()))
                     .collect();
-                let the_fn = Value::Fn::<'src>(Rc::new(crate::value::Fn::<'src> {
+                let the_fn = Value::Fn::<'src>(Rc::new(RefCell::new(crate::value::Fn::<'src> {
                     name: name.to_string(),
                     body: clauses,
                     doc,
                     enclosing,
-                }));
+                })));
-                self.bind(name.to_string(), &the_fn);
+
+                let maybe_decl_i = self.locals.iter().position(|(binding, _)| binding == name);
+
+                match maybe_decl_i {
+                    None => self.bind(name.to_string(), &the_fn),
+                    Some(i) => {
+                        let declared = &self.locals[i].1;
+                        match declared {
+                            Value::FnDecl(_) => {
+                                self.locals[i] = (name.to_string(), the_fn.clone());
+                            }
+                            _ => unreachable!("internal Ludus error"),
+                        }
+                    }
+                }
+
                 Ok(the_fn)
             }
-            FnDeclaration(_name) => Ok(Value::Nil),
+            FnDeclaration(name) => {
+                let decl = Value::FnDecl(name);
+                self.bind(name.to_string(), &decl);
+                Ok(decl)
+            }
             Panic(msg) => {
                 let msg = self.visit(msg)?;
-                Err(LErr::new(format!("{msg}")))
+                self.panic(format!("{msg}"))
             }
             Repeat(times, body) => {
                 let times_num = match self.visit(times) {
                     Ok(Value::Number(n)) => n as usize,
-                    _ => return Err(LErr::new("`repeat` may only take numbers".to_string())),
+                    _ => return self.panic("`repeat` may only take numbers".to_string()),
                 };
                 for _ in 0..times_num {
                     self.visit(body)?;

src/value.rs

@@ -30,7 +30,8 @@ pub enum Value<'src> {
     List(Vector<Self>),
     Dict(HashMap<&'static str, Self>),
     Box(&'static str, Rc<RefCell<Self>>),
-    Fn(Rc<Fn<'src>>),
+    Fn(Rc<RefCell<Fn<'src>>>),
+    FnDecl(&'static str),
     Base(BaseFn<'src>),
     Recur(Vec<Self>),
     // Set(HashSet<Self>),
@@ -57,6 +58,7 @@ impl<'src> Clone for Value<'src> {
             Value::Tuple(t) => Value::Tuple(t.clone()),
             Value::Args(a) => Value::Args(a.clone()),
             Value::Fn(f) => Value::Fn(f.clone()),
+            Value::FnDecl(name) => Value::FnDecl(name),
             Value::List(l) => Value::List(l.clone()),
             Value::Dict(d) => Value::Dict(d.clone()),
             Value::Box(name, b) => Value::Box(name, b.clone()),
@@ -71,12 +73,13 @@ impl fmt::Display for Value<'_> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
             Value::Nil => write!(f, "nil"),
-            Value::Boolean(b) => write!(f, "{}", b),
+            Value::Boolean(b) => write!(f, "{b}"),
-            Value::Number(n) => write!(f, "{}", n),
+            Value::Number(n) => write!(f, "{n}"),
-            Value::Keyword(k) => write!(f, ":{}", k),
+            Value::Keyword(k) => write!(f, ":{k}"),
-            Value::InternedString(s) => write!(f, "\"{}\"", s),
+            Value::InternedString(s) => write!(f, "\"{s}\""),
-            Value::AllocatedString(s) => write!(f, "\"{}\"", s),
+            Value::AllocatedString(s) => write!(f, "\"{s}\""),
-            Value::Fn(fun) => write!(f, "fn {}", fun.name),
+            Value::Fn(fun) => write!(f, "fn {}", fun.borrow().name),
+            Value::FnDecl(name) => write!(f, "fn {name}"),
             Value::Tuple(t) | Value::Args(t) => write!(
                 f,
                 "({})",
@@ -138,7 +141,9 @@ impl<'src> PartialEq for Value<'src> {
             (Value::List(x), Value::List(y)) => x == y,
             (Value::Dict(x), Value::Dict(y)) => x == y,
             // reference equality types
-            (Value::Fn(x), Value::Fn(y)) => Rc::<Fn<'_>>::as_ptr(x) == Rc::<Fn<'_>>::as_ptr(y),
+            (Value::Fn(x), Value::Fn(y)) => {
+                Rc::<RefCell<Fn<'_>>>::as_ptr(x) == Rc::<RefCell<Fn<'_>>>::as_ptr(y)
+            }
             (Value::Box(_, x), Value::Box(_, y)) => {
                 Rc::<RefCell<Value<'_>>>::as_ptr(x) == Rc::<RefCell<Value<'_>>>::as_ptr(y)
             }
@@ -174,7 +179,8 @@ impl Value<'_> {
                 .map(|(k, v)| format!(":{} {}", k, v.interpolate()))
                 .collect::<Vec<_>>()
                 .join(", "),
-            Value::Fn(x) => format!("fn {}", x.name),
+            Value::Fn(x) => format!("fn {}", x.borrow().name),
+            Value::FnDecl(name) => format!("fn {name}"),
             Value::Placeholder => unreachable!(),
             Value::Args(_) => unreachable!(),
             Value::Recur(_) => unreachable!(),