[Haskell-beginners] Y-combinator

[Brent Yorgey]

On Thu, Feb 25, 2010 at 03:32:25AM +0000, Jon Harrop wrote:
> On Thursday 25 February 2010 00:31:59 Brent Yorgey wrote:
> > On Wed, Feb 24, 2010 at 11:53:50PM +0000, Jon Harrop wrote:
> >
> > Haskell has recursive types, but they are iso-recursive rather than
> > equi-recursive; the recursion must always be guarded by a data
> > constructor.  I am not sure what you mean by saying that Data.Function
> > contains a "workaround".
> 
> Guarding the recursion with a constructor is the workaround I was referring 
> to, like this:
> 
> # let fix f =
>     (fun (`X x) -> f(x (`X x))) (`X(fun (`X x) y -> f(x (`X x)) y));;
> val fix : (('a -> 'b) -> 'a -> 'b) -> 'a -> 'b = <fun>
>
> > What exactly are you trying to do? 
> 
> I'm wondering if it is possible to get this to type in Haskell without 
> altering the code, i.e. by enabling recursive types in the compiler as I did 
> with OCaml using -rectypes.

No, it isn't.  There's no equivalent of -rectypes in any Haskell
compiler I'm aware of.

-Brent