Change BoolObj::new to return a Gc pointer, add T and F builtins

Since we're able to coerce objects easily, we're changing bools to be
interned behind the scenes.

T and F builtin functions are added because that's probably the easiest
way to implement true and false constants without making new
lexer/parsing rules.

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

src/obj/bool.rs

@@ -1,7 +1,7 @@
 use crate::obj::{Obj, VTable};
 use crate::syn::span::Span;
 use crate::vm::{error::*, machine::Machine};
-use gc::{Finalize, Trace};
+use gc::{Finalize, Gc, Trace};
 
 pub type Bool = bool;
 
@@ -12,11 +12,14 @@ pub struct BoolObj {
 }
 
 impl BoolObj {
-    pub fn new(value: Bool) -> Self {
-        BoolObj {
-            value,
-            vtable: vtable! {},
+    pub fn new(value: Bool) -> Gc<Self> {
+        thread_local! {
+            static BOOLS: [Gc<BoolObj>; 2] = [
+                Gc::new(BoolObj { value: false, vtable: vtable! {} }),
+                Gc::new(BoolObj { value: true, vtable: vtable! {} }),
+            ];
         }
+        BOOLS.with(|bools| Gc::clone(&bools[value as usize]))
     }
 
     #[allow(dead_code)]

src/vm/builtins.rs

@@ -1,4 +1,4 @@
-use crate::obj::{builtin::BuiltinExit, str::StrObj, Obj};
+use crate::obj::prelude::*;
 use crate::vm::{
     error::RuntimeError,
     machine::{Machine, MachineBuilder},
@@ -22,6 +22,16 @@ impl MachineBuilder {
             panic!();
         });
 
+        self.register_builtin_fun("T", |machine, _| {
+            machine.stack_push(BoolObj::new(true))?;
+            Ok(BuiltinExit::Return)
+        });
+
+        self.register_builtin_fun("F", |machine, _| {
+            machine.stack_push(BoolObj::new(false))?;
+            Ok(BuiltinExit::Return)
+        });
+
         /*
         //
         // if