Y Combinator in Haskell

Question

Is it possible to write the Y Combinator in Haskell?

It seems like it would have an infinitely recursive type.

 Y :: f -> b -> c
 where f :: (f -         


        

Answer 1

Just to make rampion's code more readable:

-- Mu :: (Mu a -> a) -> Mu a
newtype Mu a = Mu (Mu a -> a) 

w :: (Mu a -> a) -> a
w h = h (Mu h)

y :: (a -> a) -> a
y f = w (\(Mu x) -> f (w x))
-- y f = f . y f

in which w stands for the omega combinator w = \x -> x x, and y stands for the y combinator y = \f -> w . (f w).