get binding & pretty debugging working

bytecode_thoughts.md

@@ -84,4 +84,50 @@ let number = ((first as u16) << 8) | second as u16;
 #### Oy, stacks and expressions
 One thing that's giving me grief is when to pop and when to note on the value stack.
 
-Consider 
+So, like, we need to make sure that a line of code leaves the stack exactly where it was before it ran, with the exception of binding forms: `let`, `fn`, `box`, etc. Those leave one (or more!) items on the stack.
+
+In the simplest case, we have a line of code that's just a constant:
+
+```
+false
+```
+This should emit the bytecode instructions (more or less):
+```
+push false
+pop
+```
+The push comes from the `false` value. 
+The pop comes from the end of a (nonbinding) line.
+
+The problem is that there's no way (at all, in Ludus) to distinguish between an expression that's just a constant and a line that is a complete line of code that's an expression.
+
+So if we have the following:
+```
+let foo = false
+```
+We want:
+```
+push false
+```
+Or, rather, given that `foo` is a word pattern, what we actually want is:
+```
+push false # constant
+push pattern/word # load pattern
+pop
+pop # compare
+push false # for the binding
+```
+
+But it's worth it here to explore Ludus's semantics.
+It's the case that there are actually only three binding forms (for now): `let`, `fn`, and `box`. 
+Figuring out `let` will help a great deal. 
+Match also binds things, but at the very least, match doesn't bind with expressions on the rhs, but a single value.
+
+Think, too about expressions: everything comes down to a single value (of course), even tuples (especially now that I'm separating function calls from tuple values (probably)).
+So: anything that *isn't* a binding form should, before the `pop` from the end of a line, only leave a single value on the stack.
+Which suggests that, as odd as it is, pushing a single `nil` onto the stack, just to pop it, might make sense.
+Or, perhaps the thing to do is to peek: if the line in question is binding or not, then emit different bytecode.
+That's probably the thing to do. Jesus, Scott.
+
+And **another** thing worth internalizing: every single instruction that's not an explicit push or pop should leave the stack length unchanged.
+So store and load need always to swap in a `nil`

src/compiler.rs

@@ -54,6 +54,16 @@ pub struct Chunk<'a> {
     pub name: &'static str,
 }
 
+fn is_binding(expr: &Spanned<Ast>) -> bool {
+    let (ast, _) = expr;
+    use Ast::*;
+    match ast {
+        Let(..) | LBox(..) => true,
+        Fn(name, ..) => *name != "*anon",
+        _ => false,
+    }
+}
+
 impl<'a> Chunk<'a> {
     pub fn new(ast: &'a Spanned<Ast>, name: &'static str, src: &'static str) -> Chunk<'a> {
         Chunk {
@@ -114,12 +124,10 @@ impl<'a> Chunk<'a> {
     }
 
     fn bind(&mut self, name: &'static str) {
-        println!("binding {name} at depth {}", self.scope_depth);
         self.bindings.push(Binding {
             name,
             depth: self.scope_depth,
         });
-        println!("{:?}", self.bindings)
     }
 
     pub fn compile(&mut self) {
@@ -144,11 +152,15 @@ impl<'a> Chunk<'a> {
             }
             Block(lines) => {
                 self.scope_depth += 1;
-                println!("now entering scope level {}", self.scope_depth);
-                for expr in lines {
-                    self.visit(expr);
-                    self.emit_op(Op::Pop);
+                for expr in lines.iter().take(lines.len() - 1) {
+                    if is_binding(expr) {
+                        self.visit(expr)
+                    } else {
+                        self.visit(expr);
+                        self.emit_op(Op::Pop);
+                    }
                 }
+                self.visit(lines.last().unwrap());
                 self.emit_op(Op::Store);
                 self.scope_depth -= 1;
                 while let Some(binding) = self.bindings.last() {
@@ -178,7 +190,6 @@ impl<'a> Chunk<'a> {
                 self.bytecode[jump_idx + 1] = jump_offset as u8;
             }
             Let(patt, expr) => {
-                println!("let binding!");
                 self.visit(expr);
                 self.visit(patt);
             }
@@ -186,12 +197,9 @@ impl<'a> Chunk<'a> {
                 self.bind(name);
             }
             Word(name) => {
-                println!("resolving binding {name}");
-                println!("current bindings {:?}", self.bindings);
                 self.emit_op(Op::PushBinding);
                 let biter = self.bindings.iter().enumerate().rev();
                 for (i, binding) in biter {
-                    println!("at index {i}");
                     if binding.name == *name {
                         self.bytecode.push(i as u8);
                         break;
@@ -230,4 +238,25 @@ impl<'a> Chunk<'a> {
             }
         }
     }
+
+    pub fn dissasemble_instr(&self, i: usize) {
+        let op = Op::from_u8(self.bytecode[i]).unwrap();
+        use Op::*;
+        match op {
+            Pop | Store | Load => println!("{i:04}: {op}"),
+            Constant => {
+                let next = self.bytecode[i + 1];
+                let value = &self.constants[next as usize].show(self);
+                println!("{i:04}: {:16} {next:04}: {value}", op.to_string());
+            }
+            PushBinding => {
+                let next = self.bytecode[i + 1];
+                println!("{i:04}: {:16} {next:04}", op.to_string());
+            }
+            Jump | JumpIfFalse => {
+                let next = self.bytecode[i + 1];
+                println!("{i:04}: {:16} {next:04}", op.to_string())
+            }
+        }
+    }
 }

src/main.rs

@@ -1,5 +1,8 @@
 use chumsky::{input::Stream, prelude::*};
 
+const DEBUG_COMPILE: bool = true;
+const DEBUG_RUN: bool = true;
+
 mod memory_sandbox;
 
 mod spans;
@@ -41,7 +44,14 @@ pub fn run(src: &'static str) {
 
     let mut chunk = Chunk::new(&parsed, "test", src);
     chunk.compile();
-    chunk.disassemble();
+    if DEBUG_COMPILE {
+        chunk.disassemble();
+        println!("\n\n")
+    }
+
+    if DEBUG_RUN {
+        println!("=== vm run: test ===");
+    }
 
     let mut vm = Vm::new(&chunk);
     let result = vm.interpret();
@@ -58,15 +68,9 @@ let foo = :let_foo
 
 let bar = if true
     then {
-        :foo
-        :bar
-        :baz
-    }
-    else {
-        1
-        2
-        3
+        let baz = :baz
     }
+    else :whatever
 
 foo
 

src/parser.rs

@@ -922,7 +922,7 @@ where
 
     let lambda = just(Token::Reserved("fn"))
         .ignore_then(fn_unguarded.clone())
-        .map_with(|clause, e| (Fn("anonymous", vec![clause], None), e.span()));
+        .map_with(|clause, e| (Fn("*anon", vec![clause], None), e.span()));
 
     let fn_clauses = fn_clause
         .clone()

src/value.rs

@@ -41,6 +41,21 @@ pub enum Value {
     Fn(Rc<RefCell<LFn>>),
 }
 
+impl std::fmt::Display for Value {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        use Value::*;
+        match self {
+            Nil => write!(f, "nil"),
+            True => write!(f, "true"),
+            False => write!(f, "false"),
+            Keyword(idx) => write!(f, ":{idx}"),
+            Interned(idx) => write!(f, "\"@{idx}\""),
+            Number(n) => write!(f, "{n}"),
+            _ => todo!(),
+        }
+    }
+}
+
 impl Value {
     pub fn show(&self, ctx: &Chunk) -> String {
         use Value::*;

src/vm.rs

@@ -44,20 +44,35 @@ impl<'a> Vm<'a> {
     }
 
     pub fn push(&mut self, value: Value) {
-        println!("{:04} pushing {value:?}", self.ip);
         self.stack.push(value);
     }
 
     pub fn pop(&mut self) -> Value {
-        let value = self.stack.pop().unwrap();
-        println!("{:04} popping {value:?}", self.ip);
-        value
+        self.stack.pop().unwrap()
+    }
+
+    fn print_stack(&self) {
+        let inner = self
+            .stack
+            .iter()
+            .map(|val| val.to_string())
+            .collect::<Vec<_>>()
+            .join("|");
+        println!("{:04}: [{inner}] {}", self.ip, self.return_register);
+    }
+
+    fn print_debug(&self) {
+        self.chunk.dissasemble_instr(self.ip);
+        self.print_stack();
     }
 
     pub fn interpret(&mut self) -> Result<Value, Panic> {
         let Some(byte) = self.chunk.bytecode.get(self.ip) else {
             return Ok(self.stack.pop().unwrap());
         };
+        if crate::DEBUG_RUN {
+            self.print_debug();
+        }
         let op = Op::from_u8(*byte).unwrap();
         use Op::*;
         match op {
@@ -107,7 +122,16 @@ impl<'a> Vm<'a> {
             }
             Load => {
                 let mut value = Value::Nil;
+                // println!(
+                //     "before swap, return register holds: {}",
+                //     self.return_register
+                // );
                 swap(&mut self.return_register, &mut value);
+                // println!(
+                //     "before swap, return register holds: {}",
+                //     self.return_register
+                // );
+                // println!("now local value holds {value}");
                 self.push(value);
                 self.ip += 1;
                 self.interpret()