Implement stack unwinding

valuescript_vm/src/array_higher_functions/array_mapping_frame.rs

@@ -137,4 +137,8 @@ impl StackFrameTrait for ArrayMappingFrame {
   fn get_call_result(&mut self) -> CallResult {
     panic!("Not appropriate for MapFrame")
   }
+
+  fn catch_exception(&mut self, _exception: Val) -> bool {
+    return false;
+  }
 }

valuescript_vm/src/array_higher_functions/array_reduce.rs

@@ -105,4 +105,8 @@ impl StackFrameTrait for ReduceFrame {
   fn get_call_result(&mut self) -> CallResult {
     panic!("Not appropriate for ReduceFrame")
   }
+
+  fn catch_exception(&mut self, _exception: Val) -> bool {
+    return false;
+  }
 }

valuescript_vm/src/array_higher_functions/array_reduce_right.rs

@@ -119,4 +119,8 @@ impl StackFrameTrait for ReduceRightFrame {
   fn get_call_result(&mut self) -> CallResult {
     panic!("Not appropriate for ReduceRightFrame")
   }
+
+  fn catch_exception(&mut self, _exception: Val) -> bool {
+    return false;
+  }
 }

valuescript_vm/src/array_higher_functions/array_sort.rs

@@ -304,4 +304,8 @@ impl StackFrameTrait for SortFrame {
   fn get_call_result(&mut self) -> CallResult {
     panic!("Not appropriate for SortFrame")
   }
+
+  fn catch_exception(&mut self, _exception: Val) -> bool {
+    return false;
+  }
 }

valuescript_vm/src/bytecode_stack_frame.rs

@@ -445,6 +445,10 @@ impl StackFrameTrait for BytecodeStackFrame {
   fn get_call_result(&mut self) -> CallResult {
     panic!("Not appropriate for BytecodeStackFrame")
   }
+
+  fn catch_exception(&mut self, _exception: Val) -> bool {
+    return false; // TODO
+  }
 }
 
 enum ThisArg {

valuescript_vm/src/first_stack_frame.rs

@@ -36,4 +36,8 @@ impl StackFrameTrait for FirstStackFrame {
   fn get_call_result(&mut self) -> CallResult {
     return self.call_result.clone();
   }
+
+  fn catch_exception(&mut self, _exception: Val) -> bool {
+    panic!("Not appropriate for FirstStackFrame");
+  }
 }

valuescript_vm/src/stack_frame.rs

@@ -22,4 +22,5 @@ pub trait StackFrameTrait {
   fn step(&mut self) -> FrameStepResult;
   fn apply_call_result(&mut self, call_result: CallResult);
   fn get_call_result(&mut self) -> CallResult;
+  fn catch_exception(&mut self, exception: Val) -> bool;
 }

valuescript_vm/src/virtual_machine.rs

@@ -50,7 +50,12 @@ impl VirtualMachine {
   }
 
   pub fn step(&mut self) -> Result<(), Val> {
-    match self.frame.step()? {
+    let step_ok = match self.frame.step() {
+      Ok(step_ok) => step_ok,
+      Err(e) => return self.handle_exception(e),
+    };
+
+    match step_ok {
       FrameStepOk::Continue => {}
       FrameStepOk::Pop(call_result) => {
         self.pop();
@@ -74,4 +79,22 @@ impl VirtualMachine {
     let mut old_frame = self.stack.pop().unwrap();
     std::mem::swap(&mut self.frame, &mut old_frame);
   }
+
+  pub fn handle_exception(&mut self, exception: Val) -> Result<(), Val> {
+    while !self.stack.is_empty() {
+      let handled = self.frame.catch_exception(exception.clone());
+
+      if handled {
+        return Ok(());
+      }
+
+      if self.stack.is_empty() {
+        return Err(exception);
+      }
+
+      self.pop();
+    }
+
+    Err(exception)
+  }
 }