Fix VM reset after runtime error, closes #207

numbat/src/interpreter.rs

@@ -115,7 +115,7 @@ mod tests {
 
         @aliases(Hz: short)
         unit hertz: Frequency = 1 / second
-        
+
         fn sin(x: Scalar) -> Scalar
         fn atan2<D>(y: D, x: D) -> Scalar
         fn mean<D>(xs: D…) -> D

numbat/src/vm.rs

@@ -495,14 +495,15 @@ impl Vm {
     }
 
     pub fn run(&mut self, ctx: &mut ExecutionContext) -> Result<InterpreterResult> {
+        let old_stack = self.stack.clone();
         let result = self.run_without_cleanup(ctx);
         if result.is_err() {
             // Perform cleanup: clear the stack and move IP to the end.
             // This is useful for the REPL.
             //
             // TODO(minor): is this really enough? Shouldn't we also remove
             // the bytecode?
-            self.stack.clear();
+            self.stack = old_stack;
 
             // Reset the call stack
             // TODO: move the following to a function?

numbat/tests/interpreter.rs

@@ -121,6 +121,18 @@ fn test_implicit_conversion() {
     expect_failure("x2", "Unknown identifier 'x2'");
 }
 
+#[test]
+fn test_reset_after_runtime_error() {
+    let mut ctx = get_test_context();
+
+    let _ = ctx.interpret("let x = 1", CodeSource::Internal).unwrap();
+    let res = ctx.interpret("1/0", CodeSource::Internal);
+
+    assert!(res.is_err());
+
+    expect_output_with_context(&mut ctx, "x", "1");
+}
+
 #[test]
 fn test_function_inverses() {
     expect_output("sin(asin(0.1234))", "0.1234");