From: William James <w_a_x_man@...>
Date: 2008-11-07T12:33:11+09:00
Subject: Re: Redefine while

Pascal J. Bourguignon wrote:

> Emil Sandin <esandin@gmail.com> writes:
> 
> > Jason Roelofs wrote:
> >> On Thu, Nov 6, 2008 at 10:00 AM, Emil Sandin <esandin@gmail.com>
> wrote:  >>>  yield if condition
> >>> --
> >>> Posted via http://www.ruby-forum.com/.
> > > > 
> > > > 
> >> 
> >> Not possible. 'while' is a keyword, not a method.
> >> 
> >> Jason
> > 
> > Too bad. I thought you could do anything with ruby ;)
> 
> No.  You'd need a non-broken lisp to do that.

No, you wouldn't.  For real extensibility, you need Forth.

> 
> In Common Lisp:

A.k.a. Commune Lisp, Committee Lisp, and COBOL Lisp.

> 
> (shadow 'while)
> (defmacro while (condition &body body)
>    `(progn
>        (format t "In redefined while~%")
>        (when ,condition 
>          ,@body)))
> 
> (while t
>   'hi)
> In redefined while
> HI

GForth:

variable x

: try1   2 x !
  begin
    x @ 9 <
  while
    x @ .
    1 x +!
  repeat ;

: repeat  2drop drop postpone then ; immediate

: try2   2 x !
  begin
    x @ 9 <
  while
    x @ .
    1 x +!
  repeat ;

try1 cr try2

2 3 4 5 6 7 8 redefined REPEAT with repeat
2