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