protected override void HandleYield(AccessorOrMutator value)
 {
     throw new NotImplementedException();
 }
 protected override Mutator HandleReturn(AccessorOrMutator value)
 {
     return(value.GetMutator(this).Cast(_returnType));
 }
 protected override void HandleYield(AccessorOrMutator value)
 {
     AddOutput(value.GetMutator(this).CreateUpdate());
 }
 protected override STbRule <Expr> HandleReturn(AccessorOrMutator value)
 {
     throw new NotImplementedException();
 }
 protected abstract void HandleYield(AccessorOrMutator value);
 protected abstract T HandleReturn(AccessorOrMutator value);