Macaroni is better than spaghetti

We present a stack implementation of multiple environments similar in principle to that of Bobrow and Wegbreit, but based on a model which provides both static and dynamic scoping. We note some of the pragmatic consequences of this choice of models; one is that no unnecessary control stack is retained for certain important constructions such as “upward funargs” and coroutines. We also discuss the correct treatment of exit functions, and the need for “entry functions” if dynamic switching of control contexts is to be consistent.