Re: relaxed instance rules spec (was: the MPTC Dilemma (please solve))

On 3/7/06, Ben Rudiak-Gould wrote: # John Meacham wrote: # # Polymorphic recursion allows the construction of infinite types if I # # understand what you mean. # # No, that's different. An infinite type can't be written in (legal) Haskell. Though GHC with existentials allows something infinite looking (and not just because I named it "Inf" :-)):

{-# OPTIONS -fglasgow-exts #-}

data Zero = Zero data Succ n = Succ n

-- Error: infinite type! -- x = Succ x

data Inf = forall n . Inf n y = Inf (Succ y)

Jim