On Sun, Oct 2, 2011 at 2:17 PM,
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?
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