Add List.extend and List.to_list, plus some more tests

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

src/obj/list.rs

@@ -125,7 +125,7 @@ impl List {
                 if index == this.list().len() {
                     // if this is the last item in the list, then we're done
                     let new_str = format!("{}{}]", build_str.borrow(), repr_str.borrow());
-                    FunctionResult::ReturnPush(Str::create(new_str))
+                    Str::create(new_str).into()
                 } else {
                     // otherwise, continue building the string and calling to_repr
                     let new_str = format!("{}{}, ", build_str.borrow(), repr_str.borrow());
@@ -145,6 +145,13 @@ impl List {
         }
     }
 
+    pub(crate) fn to_list(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        // create a clone of this list
+        let this = vm.frame_stack()[0].clone();
+        let list_items = with_obj_downcast(this, |list: &List| list.list().clone());
+        List::create(list_items).into()
+    }
+
     impl_do_call!(to_list);
 
     pub(crate) fn init(_vm: &mut Vm, _state: FunctionState) -> FunctionResult {
@@ -182,7 +189,7 @@ impl List {
             }
         });
 
-        FunctionResult::ReturnPush(item)
+        item.into()
     }
 
     pub(crate) fn len(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
@@ -195,7 +202,7 @@ impl List {
         let this = vm.frame_stack()[0].clone();
         let arg = vm.frame_stack()[1].clone();
         with_obj_downcast_mut(this, |list: &mut List| list.list_mut().push(arg));
-        FunctionResult::ReturnPush(Nil::create())
+        Nil::create().into()
     }
 
     pub(crate) fn pop(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
@@ -210,6 +217,27 @@ impl List {
             todo!("throw an exception when the list is empty and there is nothing to pop")
         };
 
-        FunctionResult::ReturnPush(last)
+        last.into()
+    }
+
+    pub(crate) fn extend(vm: &mut Vm, _state: FunctionState) -> FunctionResult {
+        let this = vm.frame_stack()[0].clone();
+        let arg = vm.frame_stack()[1].clone();
+
+        // we have to clone here, in case this and arg are the same list. otherwise, we couldn't
+        // borrow `this` mutably while using `list` immutably.
+        let list_extension = if let Some(list) = arg.borrow().as_any().downcast_ref::<List>() {
+            list.list().clone()
+        } else {
+            // TODO List::extend - throw an exception when the argument is not a list
+            // BLOCKED-ON: exceptions
+            todo!("throw an exception when the List.extend argument is not a list")
+        };
+
+        with_obj_downcast_mut(this, |list: &mut List| {
+            list.list_mut().extend(list_extension);
+        });
+
+        Nil::create().into()
     }
 }