# Re: [stack] Rewriting System

## Manfred von Thun — 2001-07-02 02:38:26

    On Sun, 1 Jul 2001, Jack Waugh wrote:

     > In the paper on the rewriting system for Joy, I find:

    >

    > 	newstack stack  =>  [].

    >

    > This doesn't look right.  Doesn't => mean I can substitute in all

    > cases the expression on the right for that on the left, and wind up

    > with a program that denotes the same function?  Here, the expression

    > on the left denotes a function that eats up the stack and leaves only

    > the empty list on top, i. e., the same effect as "newstack []".  But

    > the program on the right, [], means push [] on top of whatever was

    > already on the stack, without clearing the stack first.  That's a

    > different function from stacks to stacks.  What did I misunderstand?

     You are exactly right. What I wrote in that paper is wrong. It should be

                    newstack stack  =>  newstack []

    I can fix that straight away in the web page. Thanks for pointing it out.

      - Manfred