Lennart Augustsson wrote:
The values Z, S Z, and S (S Z) all have the same runtime representation and there is no linear increase in size when you add a extra S.
BUT, if you make something overloaded and there is a dictionary associated with the type (Z, S Z, or S (S Z)) then the dictionary takes up space, and that space is linear in the number of S constructors.
Ah yes, that makes more sense. Since your instance would look like: instance Foo a => Foo (S a) where foo :: a -> Int a dictionary for Foo (S(S Z)) would have entries for foo@(S(S Z)) and also the dictionary for Foo (S Z) which has foo@(S Z) and a dictionary for Foo Z which has... It's still something to watch out for if you're really worrying about performance. I wonder if this is documented on the wiki's section about performance anywhere, the overhead for inductive type class instances I mean. -- Live well, ~wren