Y

yfix.hs

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

out :: Mu a -> (Mu a -> a)
out (In f) = f

omega = \f->(out f) f
psi   = \h -> \f-> h ((out f) f)
yfix   = \i-> omega (In (psi i))

factorial = yfix (\g-> \n->if n < 2 then 1 else n*( g (n-1)))

{-
fix f = fixH (In fixH)
  where 
    {-# NOINLINE fixH #-}
    fixH x = f ((out x) x)

alpha = \f n-> if (n<2) then 1 else n * ((out f) f (n-1))

omega::(Mu a->a) -> a
omega = \f-> out f f
aux = \f n->if (n < 2) then 1 else n * f (n-1)
factorial = fix $ \f n->if (n < 2) then 1 else n * f (n-1)
main = print (factorial 4)
-}