Add call site discovery to call frames, and add call stack error messages

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/vm/machine.rs

@@ -1,7 +1,7 @@
 use crate::compile::Compile;
 use crate::object::*;
 use crate::scope::*;
-use crate::syn::ast::SpStmt;
+use crate::syn::{ast::SpStmt, span::Span};
 use crate::vm::{error::*, inst::*};
 use std::cell::RefCell;
 use std::collections::BTreeMap;
@@ -13,6 +13,22 @@ pub enum Frame {
     Quote(QuoteFrame),
 }
 
+impl Frame {
+    pub fn call_site(&self) -> Option<&Span> {
+        use Frame::*;
+        match self {
+            Native(frame) => Some(&frame.call_site),
+            Quote(frame) => {
+                if frame.pc >= frame.code.len() {
+                    frame.code.last().map(|inst| inst.span())
+                } else {
+                    frame.inst().map(|inst| inst.span())
+                }
+            }
+        }
+    }
+}
+
 impl From<NativeFrame> for Frame {
     fn from(other: NativeFrame) -> Self {
         Frame::Native(other)
@@ -27,6 +43,7 @@ impl From<QuoteFrame> for Frame {
 
 #[derive(Debug, Clone)]
 pub struct NativeFrame {
+    call_site: Span,
     fun: BuiltinFn,
     reentry: usize,
 }
@@ -143,7 +160,7 @@ impl Machine {
         self.call_stack.last()
     }
 
-    pub fn call_quote(&mut self, quote: Quote) {
+    fn call_quote(&mut self, quote: Quote) {
         let (_span, locals, _expr, code) = self.quote_table.get(quote);
 
         // create a new stack frame
@@ -157,8 +174,9 @@ impl Machine {
         );
     }
 
-    pub fn call_native(&mut self, native: BuiltinFn) {
+    fn call_native(&mut self, call_site: Span, native: BuiltinFn) {
         self.call_stack.push(Frame::Native(NativeFrame {
+            call_site,
             fun: native,
             reentry: 0,
         }));
@@ -176,6 +194,20 @@ impl Machine {
     // /////////////////////////////////////////////////////////////////////////
 
     pub fn eval(&mut self, stmts: Vec<SpStmt>) -> Result<()> {
+        if let Err(mut error) = self.eval_stmt_list(stmts) {
+            // go through the call stack and make the error
+            for frame in self.call_stack.iter() {
+                if let Some(call_site) = frame.call_site() {
+                    error = error.with_location(call_site.clone());
+                }
+            }
+            Err(error)
+        } else {
+            Ok(())
+        }
+    }
+
+    fn eval_stmt_list(&mut self, stmts: Vec<SpStmt>) -> Result<()> {
         // TODO - figure out the best way to figure out the call stack
         // locations, and build an error out of that
         self.scope_stack.push_scope();
@@ -202,8 +234,7 @@ impl Machine {
                     let inst = frame.inst();
                     if let Some(inst) = inst {
                         let inst = inst.clone();
-                        let span = inst.span().clone();
+                        self.eval_inst(inst)?;
-                        self.eval_inst(inst).with_location(span)?;
                     } else {
                         self.call_stack.pop();
                     }
@@ -268,7 +299,7 @@ impl Machine {
                     self.call_quote(quote);
                 }
                 Value::BuiltinFn(builtin) => {
-                    self.call_native(builtin);
+                    self.call_native(inst.span().clone(), builtin);
                 }
                 value => return Err(RuntimeError::CannotCall(value.name().to_string()).into()),
             },