Add Method type for objects

* Methods are wrappers created with an owner and a function, which
  passes the owner as the first argument when the function is called.
* Fix a small bug in the VM where the pc was being set at the wrong
  time

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

src/obj/int.rs

@@ -1,4 +1,5 @@
-use crate::obj::prelude::*;
+use crate::obj::{prelude::*, reserved::*};
+use once_cell::sync::Lazy;
 use shredder::Scan;
 use std::fmt::{Debug, Formatter, self};
 
@@ -13,14 +14,18 @@ pub struct Int {
 
 impl Int {
     pub fn new_obj(value: i64) -> ObjRef<Self> {
-        // TODO : vtable for Int
-        let obj_ref = ObjRef::new(Self {
-            value,
-            vtable: Default::default(),
-            attrs: Default::default(),
-        });
-
-        obj_ref
+        // TODO : cache int values
+        self_referring_obj! {
+            Self {
+                value,
+                vtable: Default::default(),
+                attrs: Default::default(),
+            },
+            vtable: |obj_ref: ObjRef| vtable! {
+                // TODO needs Method type so this function is given an argument when called
+                STR_MEMBER_NAME.sym => Method::new_obj(obj_ref.clone(), INT_STR_FUN.clone()),
+            }
+        }
     }
 
     pub fn value(&self) -> i64 {
@@ -37,3 +42,15 @@ impl Debug for Int {
             .finish()
     }
 }
+
+static INT_STR_FUN: Lazy<NativeFunRef> = Lazy::new(|| {
+    NativeFun::new_obj(|_callee, vm, args| {
+        read_obj!(let int_obj = &args[0]);
+        if let Some(int_obj) = std::any::Any::downcast_ref::<Int>(int_obj.as_any()) {
+            vm.push(Str::new_obj(int_obj.value.to_string()));
+        } else {
+            panic!("{:?} is not an int", int_obj)
+        }
+        crate::vm::signal::Signal::Return
+    })
+});