On Sat, Jul 10, 2010 at 6:03 PM, Paulo J. Matos <[email protected]> wrote: > Hi all, > > I have two questions regarding match. Hopefully both have an answer. > > One of the things I would like to do in a match is to in the pattern > have a variable to stand for a given pattern and at the same time be > able to match on the structure of the variable. > > For example, assume I want to match against a cons where the first > element is an a, and the second a list of b and c but I want to be > able to assign d to stand for the list of b and c. > Something like the following with some made up syntax: > (match (cons 1 (list 2 3)) > [(cons a (var d (list b c))) > d]) >> (2 3)
This is just `and': > (match (cons 1 (list 2 3)) [(cons a (and d (list b c))) d]) '(2 3) > The second question is how to deal with two equal elements in a > pattern. For simple cases it seems I can do: > (match (cons 2 3) > [(cons a a) > 'same] > [(cons a b) > 'diff]) > > but what about if I want to use a specific equality predicate. > Something like (again with made up syntax): > (match (cons my-structure1 my-structure2) > [(and (cons a a) (my-equal? a a)) > 'same] > [(cons a b) > 'diff]) See the `match-equality-test' parameter: http://docs.racket-lang.org/reference/match.html#%28def._%28%28lib._racket/match..rkt%29._match-equality-test%29%29 -- sam th [email protected] _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
