[Haskell-cafe] Re: Release plans

[Brandon Michael Moore]

On Tue, Apr 17, 2007 at 11:39:03PM -0700, Brandon Michael Moore wrote:
> On Tue, Apr 17, 2007 at 12:50:48PM +0200, Doaitse Swierstra wrote:
> > Just to show what kind of problems we are currently facing. The  
> > following type checks in our EHC compiler and in Hugs, but not in the  
> > GHC:
> > 
> > module Test where
> > 
> > data T s = forall x. T (s -> (x -> s) -> (x, s, Int))
> > 
> > run :: (forall s . T s) -> Int
> > run ts  = case ts of
> >             T g -> let (x,_, b) =  g x id
> >                    in b
> 
> Consider this additional code which also typechecks in Hugs:
> 
> v :: forall s . T s
> v = T f
> 
> f :: s -> ([s] -> s) -> ([s], s, Int)
> f v g = let x = [v] in (x, g x, 0)
> 
> due to parametricity, run v can't depend on x or g x.
> Apparently id has type [x] -> x. Are EHC and Hugs supposed
> to support equirecursive types?
> 
> Brandon

Oops, this should have been a reply to the original thread in glasgow-haskell-users.

Brandon