[plt-scheme] Algebraic patterns

Okay, you're right.  Using quote to disambiguate between function application
and data doesn't work on the left hand side of defines.

> (define (quasiquote y) 3)
> `9 
3

Paul

At Tue, 1 Oct 2002 14:49:41 -0400, Eli Barzilay wrote:
> On Oct  1, Paul Graunke wrote:
> > I would have expected something like
> >  (define `(x y) (list 1 2))
> > or
> >  (define `(,x ,y) (list 1 2))
> 
> Currently I hacked
> 
>   (define '(x y) (list 1 2))
> 
> to work, but I'm not really happy with it -- but I agree with you -- I
> think that the second one above is much better.  To do that, I think
> that the best thing would be to use the quasiquote expander itself and
> use the result -- but only do this for quasiquotes or redefining
> macros would not be possible...  (And I don't know if expand-once is
> reliable enough for this.)
> 
> 
> > Also,
> >  (define (x y) (list 1 2)) 
> > would be the same as
> >  (define x (lambda (y) (list 1 2)))
> 
> It is, unless you wrote the above meaning that `x' is a meta variable
> and that it should be true for all possible (identifier) values...
> 
> 
> > It's a bit more clunky, but quote is the usual way to distinguish
> > between using ()'s for application or lists.  Maybe a different
> > default is needed?
> 
> I'm confused.  I think that the quasiquote thing should work in any
> case -- even if you think that making (define (list x y) ...) not
> redefine `list' is a bad choice, you might consider the same decision
> limited to (define (quasiquote ...) ...) as a better one.  Or maybe
> you mean add some `define*' form that will always look at patterns?
> (Which is a bad name since the "*" doesn't do the same it does to
> `let', but define-pattern is too verbose...)
> 
> (Apologies in advance for the weird grammar in the above paragraph...)
> 
> -- 
>           ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
>                   http://www.barzilay.org/                 Maze is Life!