Reorganize using workspaces

valuescript_vm/src/stack_frame.rs

@@ -0,0 +1,23 @@
+use super::vs_value::Val;
+
+pub type StackFrame = Box<dyn StackFrameTrait>;
+
+#[derive(Clone)]
+pub struct CallResult {
+  pub return_: Val,
+  pub this: Val,
+}
+
+pub enum FrameStepResult {
+  Continue,
+  Pop(CallResult),
+  Push(StackFrame),
+}
+
+pub trait StackFrameTrait {
+  fn write_this(&mut self, this: Val);
+  fn write_param(&mut self, param: Val);
+  fn step(&mut self) -> FrameStepResult;
+  fn apply_call_result(&mut self, call_result: CallResult);
+  fn get_call_result(&mut self) -> CallResult;
+}