macros, vm, bytecode: add #[primop] await-style primop macro

fix-runtime/src/slot.rs

@@ -6,6 +6,11 @@ use gc_arena::Mutation;
 
 use crate::{Break, Forced, Machine, NixType, Step, StrictValue, Value, ValueVariant};
 
+pub struct TypeError {
+    pub expected: NixType,
+    pub got: NixType,
+}
+
 pub trait SlotContent<'gc> {
     type Ty: Into<Value<'gc>> + TryFrom<Value<'gc>> + 'gc;
 }
@@ -50,12 +55,6 @@ where
         T::Ty::try_from(m.peek(self.depth as usize)).expect("slot held a value of the wrong type")
     }
 
-    #[inline(always)]
-    pub fn read_checked<M: Machine<'gc>>(&self, m: &M) -> Result<T::Ty, NixType> {
-        let val = m.peek(self.depth as usize);
-        T::Ty::try_from(val).map_err(|_err| val.ty())
-    }
-
     #[inline(always)]
     pub fn write<M: Machine<'gc>>(&self, m: &mut M, val: T::Ty) {
         m.replace(self.depth as usize, T::Ty::into(val));