I've seen this asked before, and I think some languages support it (ML maybe?). One way to do this is with view patterns: g f C = [f C] g f (getVN -> (v, n)) = f v : g f n getVN v@(A _ n) = (v, n) getVN v@(B _ n) = (v, n) (I changed the recursive call to g - figured you meant passing along f) If you need to still have match clauses after that, for falling through when it's not something that getVN matches, then have it yield a Maybe, and match on Just. -Michael On Tue, Sep 11, 2012 at 9:43 AM, Thiago Negri wrote:

Is it possible to capture more than one constructor in a single pattern matching? I mean, is it possible to generalize the following pattern matching of A and B to a single branch?

g f C = [f C] g f v@(A _ n) = f v : g n g f v@(B _ n) = f v : g n

For example:

g f C = [f C] g f v@(A|B _ n) = f v : g n

Or:

g f v = case v of C -> [f C] A|B -> f v : g (n v)

Thanks.

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