> So there was no real reason not to implement them as function calls. Then there was no real reason not to think of them as function calls. Indeed, and this w

> So there was no real reason not to implement them as function calls. Then there was no real reason not to think of them as function calls. Indeed, and this was the insight discovered by Guy L. Steele Jr. while experimenting with implementing the Actor Model in Lisp, which was one of the insights that lead to the development of Scheme. At some point, while reading his code, he realized that actors and closures were implemented with roughly the same code, modulo alpha conversion, and thus a message pass was the same as a function call. Of course, the real message-passing called for by the Actor Model became more practical with the introduction of tail-call elimination, because that meant that the stack did not grow out of control as the actors delivered their results via messages to the next actor. I have a feeling that the discovery of closures-as-actors and the discovery of tail-call elimination went hand-in-hand, and possibly even continuation-passing style.