[racket] unstable/match

Just now, Brian Mastenbrook wrote:
> On 10/11/2011 02:19 PM, Eli Barzilay wrote:
> > 10 minutes ago, Sam Tobin-Hochstadt wrote:
> >> I don't plan to change it, but I do plan to move it to `racket/match'.
> >
> > Instead of a new keyword, why not use `equal?'?  You can then define
> > the others instead of the extra `comparator'.  Alternatively, I think
> > that `==' is a bad name, which looks confusing in useful cases like
> >
> >    (== 3 =)
> >    (== 10<)
> >
> > and I think that the order of compared arguments should change, so
> > the last one matches things that are smaller than 10, and things like
> > `memq' can be used too.  Something like
> >
> >    (?? 3 =)
> >    (?? 10<)
> >    (?? memq '(1 2 3))
> >
> 
> (?? x) looks a bit funny, doesn't it?  Would you get rid of the
> implicit comparator?

Yes, I imagined it requiring the comparator.


> And I think you meant (?? '(1 2 3) memq) in the third example, or
> for the others to be reversed to be more similar to the ?  pattern.

Right, should have been:

  (?? equal? 4)  ; what `==' currently does
  (?? = 3)
  (?? < 10)
  (?? memq '(1 2 3))

Alternatively, and I know that this is stretching it, but `?' is taken
as a keyword anyway, detecting when `?' is used in a form and turning
it into a match predicate, so the above become:

  (equal? ? 4)
  (= ? 3)
  (< ? 10)
  (memq ? '(1 2 3))

And this obviously gives you even more -- either direction is easy to
specify, and you get arbitrary arguments, not just two.

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                    http://barzilay.org/                   Maze is Life!