On Sun, Oct 2, 2011 at 2:17 PM, <sdiy...@sjtu.edu.cn> wrote: > Finally I got what I meant: > > > class ExpandTuple t where > type Result t > expand :: t->Result t > > instance (Integral a)=>ExpandTuple (a,a) where > type Result (a,a) = (a,a,a) > expand (x,y) = (x,y,1) > > instance (Integral a)=>ExpandTuple (a,a,a) where > type Result (a,a,a) = (a,a,a) > expand = id >
If I were writing this sort of function, I would simply write: > expand (x, y) = (x, y, 1) and I would leave it at that. Since your 'expand' doesn't do anything the three-tuples, I don't see why I would want to call the function with a three-tuple argument. But I don't know your full use case. Antoine > But it's so verbose (even more so than similar C++ template code I guess), > introduces an additional name (the typeclass) into the current scope, and > requires 2 extensions: TypeFamilies and FlexibleInstances.Is there a cleaner > way to do this? > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
