[racket] redex: default matching behavior of patterns

This is heavily relied on.

Robby

On Tue, May 1, 2012 at 6:45 PM, Jon Rafkind <rafkind at cs.utah.edu> wrote:
> The default matching behavior of patterns in redex will try to match duplicate pattern variables to the same term. Thus
>
> #lang racket
>
> (require redex)
>
> (define-language Z [x integer])
> (define-metafunction Z
>  simple : integer integer -> integer
>  [(simple integer integer) 1])
>
> (term (simple 1 2))
>> simple: no clauses matched for (simple 1 2)
>
> Won't match because the pattern (simple integer integer) will match the first `integer' to 1, and wants to the second reference to `integer' to the same thing. To get it to work I need to adorn the pattern variables with _1 and _2 to make them unique.
>
> (define-language Z [x integer])
> (define-metafunction Z
>  simple : integer integer -> integer
>  [(simple integer_1 integer_2) 1])
>
> I would prefer (if possible) if the default behavior treated unadorned pattern variables as fresh so that I don't have to remember to attach a suffix. I guess this might break existing programs but I can't imagine anyone really relies on this behavior (unadorned variables matching duplicate terms).
> ____________________
>  Racket Users list:
>  http://lists.racket-lang.org/users