On Wednesday 14 October 2009 5:25:10 am Roel van Dijk wrote:
With newtypes I can probably abstract even more. (newtype X a b = X (a (a b))
In fact, with GHC extensions, you don't need newtypes: {-# LANGUAGE LiberalTypeSynonyms #-} type T a = (a,a) type X f a = f (f a) f0 :: a -> T a f0 x = (x,x) f1 :: a -> X T a f1 = f0 . f0 f2 :: a -> X (X T) a f2 = f1 . f1 f3 :: a -> X (X (X T)) a f3 = f2 . f2 f4 :: a -> X (X (X (X T))) a f4 = f3 . f3
Inferring the type of f5 also stops my machine in its tracks. But I *was* able to infer the type of (f4 . f4).
:t (f4 . f4)
(f4 . f4) :: a -> T16 (T16 a)
:t f5
Yeah. Asking for the type of 'f4 . f4' doesn't seem to expand the synonyms, while checking f5 does for some reason. I'm perplexed that having f5 defined in the file doesn't trigger the explosion unless you declare a type (even in terms of X and T) or ask for its type at the prompt. -- Dan