improve panic traces; tail calls work for simpel calls

src/main.rs

@@ -75,14 +75,12 @@ pub fn run(src: &'static str) {
 pub fn main() {
     env::set_var("RUST_BACKTRACE", "1");
     let src = "
-fn nope () -> nil
+fn recursive {
-fn foo (_, _, _) -> {
+    (0) -> :done
-    nope ()
+    (n) -> recursive (0)
-    :foo
 }
-fn bar () -> foo (1, 2, 3)
 
-bar ()
+recursive (1)
 ";
     run(src);
 }

src/vm.rs

@@ -164,21 +164,28 @@ impl Vm {
         self.result.as_ref().unwrap()
     }
 
-    pub fn print_call_stack(&mut self) {
+    pub fn call_stack(&mut self) -> String {
-        println!("in {}", self.frame.function.as_fn().name());
+        let mut stack = format!("   calling {}", self.frame.function.show());
-        for frame in self.call_stack.iter() {
+        for frame in self.call_stack.iter().rev() {
-            println!("   in {}", frame.function.as_fn().name());
+            let mut name = frame.function.show();
+            name = if name == "fn user script" {
+                "user script".to_string()
+            } else {
+                name
+            };
+            stack = format!("{stack}\n   from {name}");
         }
+        stack
     }
 
     pub fn panic(&mut self, msg: &'static str) {
-        self.result = Some(Err(Panic::Str(msg)));
+        let msg = format!("{msg}\nPanic traceback:\n{}", self.call_stack());
-        self.print_call_stack();
+        self.result = Some(Err(Panic::String(msg)));
     }
 
     pub fn panic_with(&mut self, msg: String) {
+        let msg = format!("{msg}\nPanic traceback:\n{}", self.call_stack());
         self.result = Some(Err(Panic::String(msg)));
-        self.print_call_stack();
     }
 
     pub fn interpret(&mut self) {
@@ -539,21 +546,6 @@ impl Vm {
                     self.push(splatted);
                     self.ip += 2;
                 }
-                // PushDict => {
-                //     let dict_len = self.chunk().bytecode[self.ip + 1] as usize * 2;
-                //     let dict_members = self.stack.split_off(self.stack.len() - dict_len);
-                //     let mut dict = HashMap::new();
-                //     let mut dict_iter = dict_members.iter();
-                //     while let Some(kw) = dict_iter.next() {
-                //         let Value::Keyword(key) = kw else {
-                //             unreachable!()
-                //         };
-                //         let value = dict_iter.next().unwrap();
-                //         dict.insert(*key, value.clone());
-                //     }
-                //     self.push(Value::Dict(Box::new(dict)));
-                //     self.ip += 2;
-                // }
                 PushDict => {
                     self.push(Value::Dict(Box::new(HashMap::new())));
                     self.ip += 1;
@@ -657,7 +649,6 @@ impl Vm {
                     let high = self.chunk().bytecode[self.ip + 1];
                     let low = self.chunk().bytecode[self.ip + 2];
                     let jump_len = combine_bytes(high, low);
-                    // let jump_len = self.chunk().bytecode[self.ip + 1] as usize;
                     if self.matches {
                         self.ip += jump_len + 3;
                     } else {