work on things

assets/test_prelude.ld

@@ -834,7 +834,7 @@ fn slice {
 
 fn butlast {
 	"Returns a list, omitting the last element."
-	(xs as :list) -> slice (xs, 0, dec (count (xs)))
+	(xs as :list) -> base :slice (xs, 0, dec (count (xs)))
 }
 
 &&& keywords: funny names

may_2025_thoughts.md

@@ -496,9 +496,9 @@ Here's a list of things that need doing:
     - [ ] test this
     - I did not fix it.
 * [x] Dict patterns are giving me stack discipline grief. Why is stack discipline so hard?
-* [ ] This is in the service of getting turtle graphics working
+* [x] This is in the service of getting turtle graphics working
 * Other forms in the language need help:
-    * [ ] repeat needs its stack discipline updated, it currently crashes the compiler
+    * [x] repeat needs its stack discipline updated, it currently crashes the compiler
 
 ### More closure problems
 #### 2025-06-23
@@ -522,4 +522,110 @@ SOLUTION: test to see if the function has been forward-declared, and if it has,
 NEW PROBLEM: a lot of instructions in the VM don't properly offset from the call frame's stack base, which leads to weirdness when doing things inside function calls.
 
 NEW SOLUTION: create a function that does the offset properly, and replace everywhere we directly access the stack.
-This is the thing I am about to do
+This is the thing I am about to do.
+
+### I think the interpreter, uh, works?
+#### 2025-06-24
+I'm sure I'll find some small problems.
+But right now the thing works.
+At the moment, I'm thinking about how to get good error messages.
+Panics are difficult.
+And I'm worried about ariadne as the error reporting crate.
+Since it writes to stdout, it has all kinds of escape codes.
+I need a plain ass string, at least for the web frontend.
+So.
+
+Current task, however, is how to get reasonable panic error messages.
+Let's simplify the problem.
+
+First, let's get tracebacks and line numbers.
+We use Chumsky spanned ASTs.
+The span is just a range into an str.
+What I can do is pretty stupidly just generate line numbers from the spans in the compiler, and from there, get a reasonable traceback.
+So instead of using Ariadne's fancy report builder, let's just do something more what we already have here:
+
+```
+Ludus panicked! no match
+  on line 1 in input, 
+  calling: add
+  with arguments: ("foo")
+  expected match with one of:
+    ()
+    (x as :number)
+    (x as :number, y as :number)
+    (x, y, ...zs)
+    ((x1, y1), (x2, y2))
+  >>> add ("foo")
+......^
+```
+We need:
+* the location of the function call in terms of the line number
+* the arguments used
+* the patterns expected to match (special cases: `let` vs `match` vs `fn`)
+
+That means, for bookkeeping, we need:
+* In the compiler, line number
+* In the VM, the arguments
+* In the VM, the pattern AST node.
+
+In Janet-Ludus, there are only a few types of panic:
+* `fn-no-match`: no match against a function call
+* `let-no-match`: no match against a `let` binding
+* `match-no-match`: no match against a `match` form
+* `generic-panic`: everything else
+* `runtime-error`: an internal Ludus error
+
+The first three are simply formatting differences.
+There are no tracebacks.
+
+Tracebacks should be easy enough, although there's some fiddly bits.
+While it's nice to have the carret, the brutalist attempt here should be just to give us the line--since the carret isn't exactly precise in the Janet interpereter.
+And the traceback should look something like:
+
+```
+    calling foo with (:bar, :baz)
+        at line 12 in input
+    calling bar with ()  
+        at line 34 in prelude
+    calling baz with (1, 2, 3)
+        at line 12 in input
+```
+
+Which means, again: function names, ip->line conversion, and arguments.
+
+The runtime needs a representation of the patterns in _any_ matching form.
+The speed is so much greater now that I'm not so concerned about little optimizations.
+So: a chunk needs a vec of patterns-representations. (I'm thinking simply a `Vec<String>`.)
+So does a function, for `doc!`.
+Same same re: `Vec<String>`.
+A VM needs a register for the scrutinee (which with function calls is just the arguments, already captured).
+A VM also needs a register for the pattern.
+So when there's a no match, we just yank the pattern and the scrutinee out of these registers.
+
+This all seems very straightforward compared to the compiling & VM stuff.
+
+Here's some stub code I wrote for dealing with ranges, source, line numbers:
+
+```rust
+let str = "foo bar baz\nquux frob\nthing thing thing";
+let range = 0..4;
+
+println!("{}", str.get(range).unwrap());
+
+let lines: Vec<&str> = str.split_terminator("\n").collect();
+
+println!("{:?}", lines);
+
+let idx = 20;
+
+let mut line_no = 1;
+for i in 0..idx {
+    if str.chars().nth(i).unwrap() == '\n' {
+        line_no += 1;
+    }
+}
+
+println!("line {line_no}: {}", lines[line_no - 1]);
+```
+
+

sandbox.ld

@@ -1,19 +1,5 @@
-fn circle! () -> repeat 20 {
+let foo = :foo
-	fd! (2)
+
-	rt! (inv (20))
+repeat foo {
+	print! ("hi")
 }
-
-fn flower! () -> repeat 10 {
-	circle! ()
-	rt! (inv (10))
-}
-
-fn garland! () -> repeat 10 {
-	flower! ()
-	fd! (30)
-}
-
-garland! ()
-
-do turtle_commands > unbox > print!
-do turtle_state > unbox > print!

src/chunk.rs

@@ -1,5 +1,8 @@
 use crate::op::Op;
+use crate::parser::Ast;
+use crate::spans::Spanned;
 use crate::value::Value;
+use chumsky::prelude::SimpleSpan;
 use imbl::HashMap;
 use num_traits::FromPrimitive;
 use regex::Regex;
@@ -14,13 +17,32 @@ pub struct StrPattern {
 pub struct Chunk {
     pub constants: Vec<Value>,
     pub bytecode: Vec<u8>,
+    pub nodes: Vec<&'static Ast>,
+    pub spans: Vec<SimpleSpan>,
     pub keywords: Vec<&'static str>,
     pub string_patterns: Vec<StrPattern>,
     pub env: HashMap<&'static str, Value>,
     pub msgs: Vec<String>,
+    pub src: &'static str,
+    pub input: &'static str,
 }
 
 impl Chunk {
+    pub fn new(env: HashMap<&'static str, Value>, src: &'static str, input: &'static str) -> Chunk {
+        Chunk {
+            constants: vec![],
+            bytecode: vec![],
+            nodes: vec![],
+            spans: vec![],
+            keywords: vec![],
+            string_patterns: vec![],
+            env,
+            msgs: vec![],
+            src,
+            input,
+        }
+    }
+
     pub fn dissasemble_instr(&self, i: &mut usize) {
         let op = Op::from_u8(self.bytecode[*i]).unwrap();
         use Op::*;

src/compiler.rs

@@ -62,18 +62,17 @@ fn get_builtin(name: &str, arity: usize) -> Option<Op> {
     None
 }
 
-#[derive(Debug, Clone)]
+#[derive(Debug)]
 pub struct Compiler {
     pub chunk: Chunk,
     pub bindings: Vec<Binding>,
     pub scope_depth: isize,
     pub match_depth: usize,
     pub stack_depth: usize,
-    pub spans: Vec<SimpleSpan>,
-    pub nodes: Vec<&'static Ast>,
     pub ast: &'static Ast,
     pub span: SimpleSpan,
     pub src: &'static str,
+    pub input: &'static str,
     pub name: &'static str,
     pub depth: usize,
     pub upvalues: Vec<&'static str>,
@@ -101,18 +100,13 @@ impl Compiler {
         ast: &'static Spanned<Ast>,
         name: &'static str,
         src: &'static str,
+        input: &'static str,
         depth: usize,
         env: imbl::HashMap<&'static str, Value>,
         debug: bool,
     ) -> Compiler {
-        let chunk = Chunk {
+        let chunk = Chunk::new(env, src, input);
-            constants: vec![],
+
-            bytecode: vec![],
-            keywords: vec![],
-            string_patterns: vec![],
-            env,
-            msgs: vec![],
-        };
         Compiler {
             chunk,
             bindings: vec![],
@@ -120,13 +114,12 @@ impl Compiler {
             scope_depth: -1,
             match_depth: 0,
             stack_depth: 0,
-            spans: vec![],
-            nodes: vec![],
             ast: &ast.0,
             span: ast.1,
             loop_info: vec![],
             upvalues: vec![],
             src,
+            input,
             name,
             tail_pos: false,
             debug,
@@ -222,12 +215,14 @@ impl Compiler {
 
     fn emit_op(&mut self, op: Op) {
         self.chunk.bytecode.push(op as u8);
-        self.spans.push(self.span);
+        self.chunk.spans.push(self.span);
+        self.chunk.nodes.push(self.ast);
     }
 
     fn emit_byte(&mut self, byte: usize) {
         self.chunk.bytecode.push(byte as u8);
-        self.spans.push(self.span);
+        self.chunk.spans.push(self.span);
+        self.chunk.nodes.push(self.ast);
     }
 
     fn len(&self) -> usize {
@@ -1096,6 +1091,7 @@ impl Compiler {
                                 clause,
                                 name,
                                 self.src,
+                                self.input,
                                 self.depth + 1,
                                 self.chunk.env.clone(),
                                 self.debug,

src/errors.rs

@@ -1,9 +1,90 @@
 // use crate::process::{LErr, Trace};
+use crate::parser::Ast;
+use crate::spans::Spanned;
 use crate::validator::VErr;
 use crate::value::Value;
+use crate::vm::CallFrame;
 use ariadne::{sources, Color, Label, Report, ReportKind};
 use std::collections::HashSet;
 
+#[derive(Debug, Clone, PartialEq)]
+pub enum PanicInfo {
+    RepeatNumberType(Value),
+    NoMatch,
+    LetMatchFail,
+    MatchFail,
+    FnMatchFail,
+    Internal(&'static str),
+    ListSplat(Value),
+    DictSplat(Value),
+    DecType(Value),
+    WhenFail,
+    AddType(Value, Value),
+    SubType(Value, Value),
+    MultType(Value, Value),
+    DivType(Value, Value),
+    UnboxType(Value),
+    StoreType(Value),
+    Assert,
+    Explicit(Value),
+    GetType(Value),
+    AtIdxType(Value),
+    AtCollectionType(Value),
+    PartialType(Value),
+    ArityMismatch(Value, Vec<Value>),
+    CallType(Value),
+    DivisionByZero,
+}
+
+impl PanicInfo {
+    pub fn msg(&self) -> String {
+        use PanicInfo::*;
+        match self {
+            RepeatNumberType(value) => format!("`repeat` expects a number; it got `{value}`"),
+            _ => todo!(),
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct Panic {
+    pub frame: CallFrame,
+    pub call_stack: Vec<CallFrame>,
+    pub info: PanicInfo,
+}
+
+impl Panic {
+    pub fn report(&self) {
+        println!("got frame: {}", self.frame);
+        let mut srcs = HashSet::new();
+        let ast_spans = std::iter::zip(
+            self.frame.chunk().spans.iter(),
+            self.frame.chunk().nodes.iter(),
+        );
+        let ast_spans = ast_spans
+            .map(|(span, ast)| format!("{span} || {}", ast.show()))
+            .collect::<Vec<_>>()
+            .join("\n");
+        println!("{ast_spans}");
+        let msg = self.info.msg();
+        let input = self.frame.chunk().input;
+        let src = self.frame.chunk().src;
+        srcs.insert((input, src));
+        let mut traceback = format!("Ludus panicked! {msg}");
+        for frame in self.call_stack.iter().rev() {
+            let name = frame.function.as_fn().name();
+            let args = frame
+                .args
+                .iter()
+                .map(|arg| arg.show())
+                .collect::<Vec<_>>()
+                .join(", ");
+            traceback = format!("{traceback}\n  calling `{name}` with ({args})");
+        }
+        println!("{traceback}");
+    }
+}
+
 // pub fn report_panic(err: LErr) {
 //     let mut srcs = HashSet::new();
 //     let mut stack = vec![];

src/main.rs

@@ -3,8 +3,8 @@ use imbl::HashMap;
 use std::env;
 use std::fs;
 
-const DEBUG_SCRIPT_COMPILE: bool = false;
+const DEBUG_SCRIPT_COMPILE: bool = true;
-const DEBUG_SCRIPT_RUN: bool = false;
+const DEBUG_SCRIPT_RUN: bool = true;
 const DEBUG_PRELUDE_COMPILE: bool = false;
 const DEBUG_PRELUDE_RUN: bool = false;
 
@@ -73,6 +73,7 @@ pub fn prelude() -> HashMap<&'static str, Value> {
         parsed,
         "prelude",
         PRELUDE,
+        "prelude",
         0,
         HashMap::new(),
         DEBUG_PRELUDE_COMPILE,
@@ -90,7 +91,7 @@ pub fn prelude() -> HashMap<&'static str, Value> {
     }
 }
 
-pub fn run(src: &'static str) {
+pub fn run(src: &'static str, input: &'static str) {
     let (tokens, lex_errs) = lexer().parse(src).into_output_errors();
     if !lex_errs.is_empty() {
         println!("{:?}", lex_errs);
@@ -115,7 +116,7 @@ pub fn run(src: &'static str) {
     let prelude = prelude();
     // let prelude = imbl::HashMap::new();
 
-    let mut validator = Validator::new(&parsed.0, &parsed.1, "user input", src, prelude.clone());
+    let mut validator = Validator::new(&parsed.0, &parsed.1, input, src, prelude.clone());
     validator.validate();
 
     if !validator.errors.is_empty() {
@@ -124,7 +125,7 @@ pub fn run(src: &'static str) {
         return;
     }
 
-    let mut compiler = Compiler::new(parsed, "sandbox", src, 0, prelude, DEBUG_SCRIPT_COMPILE);
+    let mut compiler = Compiler::new(parsed, input, src, input, 0, prelude, DEBUG_SCRIPT_COMPILE);
     // let base = base::make_base();
     // compiler.emit_constant(base);
     // compiler.bind("base");
@@ -147,7 +148,10 @@ pub fn run(src: &'static str) {
     let result = vm.run();
     let output = match result {
         Ok(val) => val.to_string(),
-        Err(panic) => format!("Ludus panicked! {panic}"),
+        Err(panic) => {
+            panic.report();
+            std::process::exit(1)
+        }
     };
     if DEBUG_SCRIPT_RUN {
         vm.print_stack();
@@ -180,11 +184,28 @@ pub fn ld_fmt(src: &'static str) -> Result<String, String> {
 }
 
 pub fn main() {
-    env::set_var("RUST_BACKTRACE", "1");
+    // env::set_var("RUST_BACKTRACE", "1");
-    let src: &'static str = fs::read_to_string("sandbox.ld").unwrap().leak();
+    // let src: &'static str = fs::read_to_string("sandbox.ld").unwrap().leak();
-    match ld_fmt(src) {
+    // run(src, "sandbox.ld");
-        Ok(src) => println!("{}", src),
+    let str = "foo bar baz\nquux frob\nthing thing thing";
-        Err(msg) => println!("Could not format source with errors:\n{}", msg),
+    let range = 0..4;
+
+    println!("{}", range.start);
+
+    println!("{}", str.get(range).unwrap());
+
+    let lines: Vec<&str> = str.split_terminator("\n").collect();
+
+    println!("{:?}", lines);
+
+    let idx = 20;
+
+    let mut line_no = 1;
+    for i in 0..idx {
+        if str.chars().nth(i).unwrap() == '\n' {
+            line_no += 1;
         }
-    run(src);
+    }
+
+    println!("line {line_no}: {}", lines[line_no - 1]);
 }

src/parser.rs

@@ -4,35 +4,6 @@ use chumsky::{input::ValueInput, prelude::*, recursive::Recursive};
 use std::fmt;
 use struct_scalpel::Dissectible;
 
-// #[derive(Clone, Debug, PartialEq)]
-// pub struct WhenClause {
-//     pub cond: Spanned<Ast>,
-//     pub body: Spanned<Ast>,
-// }
-
-// impl fmt::Display for WhenClause {
-//     fn fmt(self: &WhenClause, f: &mut fmt::Formatter) -> fmt::Result {
-//         write!(f, "cond: {}, body: {}", self.cond.0, self.body.0)
-//     }
-// }
-
-// #[derive(Clone, Debug, PartialEq)]
-// pub struct MatchClause {
-//     pub patt: Spanned<Pattern>,
-//     pub guard: Option<Spanned<Ast>>,
-//     pub body: Spanned<Ast>,
-// }
-
-// impl fmt::Display for MatchClause {
-//     fn fmt(self: &MatchClause, f: &mut fmt::Formatter) -> fmt::Result {
-//         write!(
-//             f,
-//             "pattern: {}, guard: {:?} body: {}",
-//             self.patt.0, self.guard, self.body.0
-//         )
-//     }
-// }
-
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum StringPart {
     Data(String),
@@ -219,14 +190,12 @@ impl Ast {
                     .collect::<Vec<_>>()
                     .join("\n  ")
             ),
-            FnBody(clauses) => format!(
+            FnBody(clauses) => clauses
-                "{}",
-                clauses
                 .iter()
                 .map(|(clause, _)| clause.show())
                 .collect::<Vec<_>>()
                 .join("\n  ")
-            ),
+                .to_string(),
             Fn(name, body, doc) => {
                 let mut out = format!("fn {name} {{\n");
                 if let Some(doc) = doc {
@@ -267,7 +236,7 @@ impl Ast {
                     .join(", ")
             ),
             MatchClause(pattern, guard, body) => {
-                let mut out = format!("{}", pattern.0.show());
+                let mut out = pattern.0.show().to_string();
                 if let Some(guard) = guard.as_ref() {
                     out = format!("{out} if {}", guard.0.show());
                 }
@@ -523,75 +492,6 @@ impl fmt::Debug for StringMatcher {
     }
 }
 
-// #[derive(Clone, Debug, PartialEq)]
-// pub enum Pattern {
-//     Nil,
-//     Boolean(bool),
-//     Number(f64),
-//     String(&'static str),
-//     Interpolated(Vec<Spanned<StringPart>>, StringMatcher),
-//     Keyword(&'static str),
-//     Word(&'static str),
-//     As(&'static str, &'static str),
-//     Splattern(Box<Spanned<Self>>),
-//     Placeholder,
-//     Tuple(Vec<Spanned<Self>>),
-//     List(Vec<Spanned<Self>>),
-//     Pair(&'static str, Box<Spanned<Self>>),
-//     Dict(Vec<Spanned<Self>>),
-// }
-
-// impl fmt::Display for Pattern {
-//     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-//         match self {
-//             Pattern::Nil => write!(f, "nil"),
-//             Pattern::Boolean(b) => write!(f, "{}", b),
-//             Pattern::Number(n) => write!(f, "{}", n),
-//             Pattern::String(s) => write!(f, "{}", s),
-//             Pattern::Keyword(k) => write!(f, ":{}", k),
-//             Pattern::Word(w) => write!(f, "{}", w),
-//             Pattern::As(w, t) => write!(f, "{} as {}", w, t),
-//             Pattern::Splattern(p) => write!(f, "...{}", p.0),
-//             Pattern::Placeholder => write!(f, "_"),
-//             Pattern::Tuple(t) => write!(
-//                 f,
-//                 "({})",
-//                 t.iter()
-//                     .map(|x| x.0.to_string())
-//                     .collect::<Vec<_>>()
-//                     .join(", ")
-//             ),
-//             Pattern::List(l) => write!(
-//                 f,
-//                 "({})",
-//                 l.iter()
-//                     .map(|x| x.0.to_string())
-//                     .collect::<Vec<_>>()
-//                     .join(", ")
-//             ),
-//             Pattern::Dict(entries) => write!(
-//                 f,
-//                 "#{{{}}}",
-//                 entries
-//                     .iter()
-//                     .map(|(pair, _)| pair.to_string())
-//                     .collect::<Vec<_>>()
-//                     .join(", ")
-//             ),
-//             Pattern::Pair(key, value) => write!(f, ":{} {}", key, value.0),
-//             Pattern::Interpolated(strprts, _) => write!(
-//                 f,
-//                 "interpolated: \"{}\"",
-//                 strprts
-//                     .iter()
-//                     .map(|part| part.0.to_string())
-//                     .collect::<Vec<_>>()
-//                     .join("")
-//             ),
-//         }
-//     }
-// }
-
 fn is_word_char(c: char) -> bool {
     if c.is_ascii_alphanumeric() {
         return true;

src/vm.rs

@@ -1,8 +1,7 @@
 use crate::base::BaseFn;
 use crate::chunk::Chunk;
+use crate::errors::{Panic, PanicInfo};
 use crate::op::Op;
-use crate::parser::Ast;
-use crate::spans::Spanned;
 use crate::value::{LFn, Value};
 use imbl::{HashMap, Vector};
 use num_traits::FromPrimitive;
@@ -12,43 +11,11 @@ use std::mem::swap;
 use std::rc::Rc;
 
 #[derive(Debug, Clone, PartialEq)]
-// pub struct Panic {
-//     pub input: &'static str,
-//     pub src: &'static str,
-//     pub msg: String,
-//     pub span: SimpleSpan,
-//     pub trace: Vec<Trace>,
-//     pub extra: String,
-// }
-pub enum Panic {
-    Str(&'static str),
-    String(String),
-}
-
-impl fmt::Display for Panic {
-    fn fmt(self: &Panic, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            Panic::Str(msg) => write!(f, "{msg}"),
-            Panic::String(msg) => write!(f, "{msg}"),
-        }
-    }
-}
-
-#[derive(Debug, Clone, PartialEq)]
-pub struct Trace {
-    pub callee: Spanned<Ast>,
-    pub caller: Spanned<Ast>,
-    pub function: Value,
-    pub arguments: Value,
-    pub input: &'static str,
-    pub src: &'static str,
-}
-
 pub struct CallFrame {
     pub function: Value,
-    pub arity: u8,
     pub stack_base: usize,
     pub ip: usize,
+    pub args: Vec<Value>,
 }
 
 impl CallFrame {
@@ -56,7 +23,7 @@ impl CallFrame {
         let Value::Fn(ref function) = self.function else {
             unreachable!()
         };
-        function.chunk(self.arity)
+        function.chunk(self.args.len() as u8)
     }
 }
 
@@ -69,7 +36,7 @@ impl fmt::Display for CallFrame {
             f,
             "CallFrame: {}/{} @ {}",
             function.name(),
-            self.arity,
+            self.args.len(),
             self.ip
         )
     }
@@ -108,7 +75,7 @@ impl Vm {
             function: base_fn.clone(),
             stack_base: 0,
             ip: 0,
-            arity: 0,
+            args: vec![],
         };
         Vm {
             stack: vec![],
@@ -186,15 +153,21 @@ impl Vm {
         stack
     }
 
-    pub fn panic(&mut self, msg: &'static str) {
+    pub fn panic(&mut self, info: PanicInfo) {
-        let msg = format!("{msg}\nPanic traceback:\n{}", self.call_stack());
+        let mut frame = self.frame.clone();
-        self.result = Some(Err(Panic::String(msg)));
+        frame.ip = self.ip;
+        let panic = Panic {
+            info,
+            frame,
+            call_stack: self.call_stack.clone(),
+        };
+        self.result = Some(Err(panic));
     }
 
-    pub fn panic_with(&mut self, msg: String) {
+    // pub fn panic_with(&mut self, msg: String) {
-        let msg = format!("{msg}\nPanic traceback:\n{}", self.call_stack());
+    //     let msg = format!("{msg}\nPanic traceback:\n{}", self.call_stack());
-        self.result = Some(Err(Panic::String(msg)));
+    //     self.result = Some(Err(Panic::String(msg)));
-    }
+    // }
 
     fn get_value_at(&mut self, idx: u8) -> Value {
         let idx = idx as usize;
@@ -280,7 +253,7 @@ impl Vm {
                     match cond {
                         Value::Number(x) if x <= 0.0 => self.ip += jump_len,
                         Value::Number(..) => (),
-                        _ => return self.panic("repeat requires a number"),
+                        _ => return self.panic(PanicInfo::RepeatNumberType(cond.clone())),
                     }
                 }
                 Pop => {
@@ -358,7 +331,7 @@ impl Vm {
                 }
                 PanicIfNoMatch => {
                     if !self.matches {
-                        return self.panic("no match");
+                        return self.panic(PanicInfo::NoMatch);
                     }
                 }
                 MatchConstant => {
@@ -434,14 +407,14 @@ impl Vm {
                                 self.push(member.clone());
                             }
                         }
-                        _ => return self.panic("internal error: expected tuple"),
+                        _ => return self.panic(PanicInfo::Internal("expected tuple")),
                     };
                 }
                 LoadSplattedTuple => {
                     let load_len = self.read() as usize;
                     let tuple = self.get_scrutinee();
                     let Value::Tuple(members) = tuple else {
-                        return self.panic("internal error: expected tuple");
+                        return self.panic(PanicInfo::Internal("expected tuple"));
                     };
                     for i in 0..load_len - 1 {
                         self.push(members[i].clone());
@@ -458,8 +431,9 @@ impl Vm {
                 AppendList => {
                     let value = self.pop();
                     let list = self.pop();
-                    let Value::List(mut list) = list else {
+                    let mut list = match list {
-                        return self.panic("only lists may be splatted into lists");
+                        Value::List(mut list) => list,
+                        not_list => return self.panic(PanicInfo::ListSplat(not_list.clone())),
                     };
                     list.push_back(value);
                     self.push(Value::List(list));
@@ -470,8 +444,9 @@ impl Vm {
                     let Value::List(mut target) = target else {
                         unreachable!()
                     };
-                    let Value::List(splatted) = splatted else {
+                    let splatted = match splatted {
-                        return self.panic("only lists may be splatted into lists");
+                        Value::List(list) => list,
+                        not_list => return self.panic(PanicInfo::ListSplat(not_list.clone())),
                     };
                     target.append(*splatted);
                     self.push(Value::List(target));
@@ -503,14 +478,14 @@ impl Vm {
                                 self.push(member.clone());
                             }
                         }
-                        _ => return self.panic("internal error: expected list"),
+                        _ => return self.panic(PanicInfo::Internal("expected list")),
                     };
                 }
                 LoadSplattedList => {
                     let loaded_len = self.read() as usize;
                     let list = self.get_scrutinee();
                     let Value::List(members) = list else {
-                        return self.panic("internal error: expected list");
+                        return self.panic(PanicInfo::Internal("expected list"));
                     };
                     for i in 0..loaded_len - 1 {
                         self.push(members[i].clone());
@@ -533,11 +508,13 @@ impl Vm {
                     self.push(Value::Dict(dict));
                 }
                 ConcatDict => {
-                    let Value::Dict(splatted) = self.pop() else {
+                    let splatted = match self.pop() {
-                        return self.panic("only dicts may be splatted into dicts");
+                        Value::Dict(dict) => dict,
+                        not_dict => return self.panic(PanicInfo::DictSplat(not_dict.clone())),
                     };
-                    let Value::Dict(target) = self.pop() else {
+                    let target = match self.pop() {
-                        unreachable!()
+                        Value::Dict(dict) => dict,
+                        not_dict => return self.panic(PanicInfo::Internal("expected dict")),
                     };
                     let union = splatted.union(*target);
                     self.push(Value::Dict(Box::new(union)));
@@ -547,15 +524,12 @@ impl Vm {
                     let dict = match self.get_value_at(dict_idx) {
                         Value::Dict(dict) => dict,
                         value => {
-                            println!(
-                                "internal Ludus error in function {}",
-                                self.frame.function.as_fn().name()
-                            );
                             unreachable!("expected dict, got {value}")
                         }
                     };
-                    let Value::Keyword(key) = self.pop() else {
+                    let key = match self.pop() {
-                        unreachable!("expected keyword, got something else")
+                        Value::Keyword(key) => key,
+                        not_keyword => unreachable!("expected keyword, got {not_keyword}"),
                     };
                     let value = dict.get(&key).unwrap_or(&Value::Nil);
                     self.push(value.clone());
@@ -622,31 +596,22 @@ impl Vm {
                     let type_of = Value::Keyword(val.type_of());
                     self.push(type_of);
                 }
-                ToInt => {
+                ToInt => match self.pop() {
-                    let val = self.pop();
+                    Value::Number(x) => self.push(Value::Number(x as usize as f64)),
-                    if let Value::Number(x) = val {
+                    not_number => return self.panic(PanicInfo::RepeatNumberType(not_number)),
-                        self.push(Value::Number(x as usize as f64));
+                },
-                    } else {
+                Decrement => match self.pop() {
-                        return self.panic("repeat requires a number");
+                    Value::Number(x) => self.push(Value::Number(x - 1.0)),
-                    }
+                    not_number => return self.panic(PanicInfo::DecType(not_number)),
-                }
+                },
-                Decrement => {
-                    let val = self.pop();
-                    if let Value::Number(x) = val {
-                        self.push(Value::Number(x - 1.0));
-                    } else {
-                        return self.panic("you may only decrement a number");
-                    }
-                }
                 Duplicate => {
                     self.push(self.peek().clone());
                 }
                 MatchDepth => {
                     self.match_depth = self.read();
                 }
-                PanicNoWhen | PanicNoMatch => {
+                PanicNoWhen => return self.panic(PanicInfo::WhenFail),
-                    return self.panic("no match");
+                PanicNoMatch => return self.panic(PanicInfo::NoMatch),
-                }
                 Eq => {
                     let first = self.pop();
                     let second = self.pop();
@@ -659,65 +624,61 @@ impl Vm {
                 Add => {
                     let first = self.pop();
                     let second = self.pop();
-                    if let (Value::Number(x), Value::Number(y)) = (first, second) {
+                    match (first, second) {
-                        self.push(Value::Number(x + y))
+                        (Value::Number(x), Value::Number(y)) => self.push(Value::Number(x + y)),
-                    } else {
+                        (x, y) => return self.panic(PanicInfo::AddType(y, x)),
-                        return self.panic("`add` requires two numbers");
                     }
                 }
                 Sub => {
                     let first = self.pop();
                     let second = self.pop();
-                    if let (Value::Number(x), Value::Number(y)) = (first, second) {
+                    match (first, second) {
-                        self.push(Value::Number(y - x))
+                        (Value::Number(x), Value::Number(y)) => self.push(Value::Number(y - x)),
-                    } else {
+                        (x, y) => return self.panic(PanicInfo::SubType(y, x)),
-                        return self.panic("`sub` requires two numbers");
                     }
                 }
                 Mult => {
                     let first = self.pop();
                     let second = self.pop();
-                    if let (Value::Number(x), Value::Number(y)) = (first, second) {
+                    match (first, second) {
-                        self.push(Value::Number(x * y))
+                        (Value::Number(x), Value::Number(y)) => self.push(Value::Number(x * y)),
-                    } else {
+                        (x, y) => return self.panic(PanicInfo::MultType(y, x)),
-                        return self.panic("`mult` requires two numbers");
                     }
                 }
                 Div => {
                     let first = self.pop();
                     let second = self.pop();
-                    if let (Value::Number(x), Value::Number(y)) = (first, second) {
+                    match (first, second) {
-                        if x == 0.0 {
+                        (Value::Number(0.0), Value::Number(_)) => {
-                            return self.panic("division by 0");
+                            return self.panic(PanicInfo::DivisionByZero)
                         }
-                        self.push(Value::Number(y / x))
+                        (Value::Number(x), Value::Number(y)) => self.push(Value::Number(y / x)),
-                    } else {
+                        (x, y) => return self.panic(PanicInfo::DivType(y, x)),
-                        return self.panic("`div` requires two numbers");
                     }
                 }
                 Unbox => {
                     let the_box = self.pop();
-                    let inner = if let Value::Box(b) = the_box {
+                    let inner = match the_box {
-                        b.borrow().clone()
+                        Value::Box(b) => b.borrow().clone(),
-                    } else {
+                        not_a_box => return self.panic(PanicInfo::UnboxType(not_a_box)),
-                        return self.panic("`unbox` requires a box");
                     };
                     self.push(inner);
                 }
                 BoxStore => {
                     let new_value = self.pop();
                     let the_box = self.pop();
-                    if let Value::Box(b) = the_box {
+                    match the_box {
+                        Value::Box(b) => {
                             b.replace(new_value.clone());
-                    } else {
+                        }
-                        return self.panic("`store` requires a box");
+                        not_a_box => return self.panic(PanicInfo::StoreType(not_a_box)),
                     }
                     self.push(new_value);
                 }
                 Assert => {
                     let value = self.stack.last().unwrap();
                     if let Value::Nil | Value::False = value {
-                        return self.panic("asserted falsy value");
+                        return self.panic(PanicInfo::Assert);
                     }
                 }
                 Get => {
@@ -728,7 +689,7 @@ impl Vm {
                             d.as_ref().get(&k).unwrap_or(&Value::Nil).clone()
                         }
                         (Value::Keyword(_), _) => Value::Nil,
-                        _ => return self.panic("keys must be keywords"),
+                        (not_a_keyword, _) => return self.panic(PanicInfo::GetType(not_a_keyword)),
                     };
                     self.push(value);
                 }
@@ -742,8 +703,10 @@ impl Vm {
                         (Value::Tuple(t), Value::Number(i)) => {
                             t.get(i as usize).unwrap_or(&Value::Nil).clone()
                         }
-                        (_, Value::Number(_)) => Value::Nil,
+                        (coll, Value::Number(_)) => {
-                        _ => return self.panic("indexes must be numbers"),
+                            return self.panic(PanicInfo::AtCollectionType(coll))
+                        }
+                        (coll, idx) => return self.panic(PanicInfo::AtIdxType(idx)),
                     };
                     self.push(value);
                 }
@@ -756,8 +719,8 @@ impl Vm {
                     self.push(negated);
                 }
                 Panic => {
-                    let msg = self.pop().show();
+                    let msg = self.pop();
-                    return self.panic_with(msg);
+                    return self.panic(PanicInfo::Explicit(msg));
                 }
                 EmptyString => {
                     self.push(Value::String(Rc::new("".to_string())));
@@ -786,7 +749,7 @@ impl Vm {
                     let arity = self.read();
                     let the_fn = self.pop();
                     let Value::Fn(ref inner) = the_fn else {
-                        return self.panic("only functions may be partially applied");
+                        return self.panic(PanicInfo::PartialType(the_fn));
                     };
                     let args = self.stack.split_off(self.stack.len() - arity as usize);
                     let partial = crate::value::Partial {
@@ -810,15 +773,13 @@ impl Vm {
 
                     match called {
                         Value::Fn(_) => {
+                            let args = self.stack.split_off(self.stack.len() - arity as usize);
                             if !called.as_fn().accepts(arity) {
-                                return self.panic_with(format!(
+                                return self.panic(PanicInfo::ArityMismatch(called, args));
-                                    "wrong number of arguments to {} passing {arity} args",
-                                    called.show()
-                                ));
                             }
                             // first put the arguments in the register
                             for i in 0..arity as usize {
-                                self.return_register[arity as usize - i - 1] = self.pop();
+                                self.return_register[i] = args[i].clone();
                             }
                             // self.print_stack();
 
@@ -849,7 +810,7 @@ impl Vm {
 
                             let mut frame = CallFrame {
                                 function: called,
-                                arity,
+                                args,
                                 stack_base: self.stack.len() - arity as usize,
                                 ip: 0,
                             };
@@ -874,7 +835,9 @@ impl Vm {
                                     let x = &self.pop();
                                     f(x, y, z)
                                 }
-                                _ => return self.panic("internal ludus error"),
+                                _ => {
+                                    return self.panic(PanicInfo::Internal("no match calling base"))
+                                }
                             };
                             // // algo:
                             // // clear the stack
@@ -891,19 +854,19 @@ impl Vm {
                         }
                         Value::Partial(partial) => {
                             let last_arg = self.pop();
-                            let args = &partial.args;
+                            let mut args = partial.args.clone();
-                            for arg in args {
+                            let placeholder_idx =
-                                if *arg == Value::Nothing {
+                                args.iter().position(|arg| *arg == Value::Nothing).unwrap();
-                                    self.push(last_arg.clone());
+                            args[placeholder_idx] = last_arg;
-                                } else {
+                            for arg in args.iter() {
                                 self.push(arg.clone());
                             }
-                            }
                             let the_fn = partial.function.clone();
+                            let arity = args.len();
                             let mut frame = CallFrame {
                                 function: the_fn,
-                                arity: args.len() as u8,
+                                args,
-                                stack_base: self.stack.len() - args.len(),
+                                stack_base: self.stack.len() - arity,
                                 ip: 0,
                             };
 
@@ -913,9 +876,7 @@ impl Vm {
                             self.call_stack.push(frame);
                             self.ip = 0;
                         }
-                        _ => {
+                        _ => return self.panic(PanicInfo::CallType(called)),
-                            return self.panic_with(format!("{} is not a function", called.show()))
-                        }
                     }
                 }
                 Call => {
@@ -930,10 +891,8 @@ impl Vm {
                     match called {
                         Value::Fn(_) => {
                             if !called.as_fn().accepts(arity) {
-                                return self.panic_with(format!(
+                                let args = self.stack.split_off(self.stack.len() - arity as usize);
-                                    "wrong number of arguments to {} passing {arity} args",
+                                return self.panic(PanicInfo::ArityMismatch(called, args));
-                                    called.show()
-                                ));
                             }
                             let splat_arity = called.as_fn().splat_arity();
                             if splat_arity > 0 && arity >= splat_arity {
@@ -948,9 +907,13 @@ impl Vm {
                             } else {
                                 arity
                             };
+                            let mut args = vec![];
+                            for offset in (0..arity as usize).rev() {
+                                args.push(self.stack[self.stack.len() - offset - 1].clone());
+                            }
                             let mut frame = CallFrame {
                                 function: called,
-                                arity,
+                                args,
                                 stack_base: self.stack.len() - arity as usize,
                                 ip: 0,
                             };
@@ -976,25 +939,25 @@ impl Vm {
                                     let x = &self.pop();
                                     f(x, y, z)
                                 }
-                                _ => return self.panic("internal ludus error"),
+                                _ => unreachable!(),
                             };
                             self.push(value);
                         }
                         Value::Partial(partial) => {
                             let last_arg = self.pop();
-                            let args = &partial.args;
+                            let mut args = partial.args.clone();
-                            for arg in args {
+                            let placeholder_idx =
-                                if *arg == Value::Nothing {
+                                args.iter().position(|arg| *arg == Value::Nothing).unwrap();
-                                    self.push(last_arg.clone());
+                            args[placeholder_idx] = last_arg;
-                                } else {
+                            for arg in args.iter() {
                                 self.push(arg.clone());
                             }
-                            }
                             let the_fn = partial.function.clone();
+                            let arity = args.len();
                             let mut frame = CallFrame {
                                 function: the_fn,
-                                arity: args.len() as u8,
+                                args,
-                                stack_base: self.stack.len() - args.len(),
+                                stack_base: self.stack.len() - arity,
                                 ip: 0,
                             };
 
@@ -1004,9 +967,7 @@ impl Vm {
                             self.call_stack.push(frame);
                             self.ip = 0;
                         }
-                        _ => {
+                        _ => return self.panic(PanicInfo::CallType(called)),
-                            return self.panic_with(format!("{} is not a function", called.show()))
-                        }
                     }
                 }
                 Return => {