Oh, that make sense! 2009/6/25 José Pedro Magalhães <[email protected]>
> Hey David, > > For instance: > > arity :: (Data a) => a -> Int >> arity = length . gmapQ (const ()) >> > > > Cheers, > Pedro > > On Thu, Jun 25, 2009 at 17:31, David Fox <[email protected]> wrote: > >> Is it possible to determine the arity of a value's constructor? >> Suppose I have a value x of type >> >> data A = B Int | C >> >> They typeOf function returns its TypeRep, which contains its type >> constructor, but I don't see how to decide whether that >> constructor's arity is 0 or 1. If the type has field names >> I can look at those using Data.Data.conFields and count them, >> but if it doesn't I don't see how to do it. >> >> -david >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> [email protected] >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >
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