> > (3) OK with GHC, error with Hugs:
> >
> > f = \x -> m x
> > x = f()
> ...
> > - Is GHC's treatment of (3) a bug?
>
> At first glance it looks a bit that way to me, but
> I will leave it for the more knowledgable Haskell experts
> to give you a definitive answer on that one.
IIRC it's a known bug in Hugs, and fixing it would be difficult as it is an artifact
of the typechecking algorithm used.
GHC is correct, because f *is* monomorphic: the only use is at type (). Thus f is
given the type () -> (), rather than C a => a -> (), and thus no sharing is lost.
However, detecting that f is only used at the one type involves sneaky look-ahead.
The monomorphism restriction is described in the Haskell Report (at www.haskell.org)
in section 4.5.5. I was going to give a reference to the relevant message on the
Hugs-bugs or Hugs-users list, but I can't find it because the archive page has been
split into 51 pages and I'm not going to search all of them! [hugs-bugs moderator
please take note!]
HTH.
--KW 8-)
--
: Keith Wansbrough, MSc, BSc(Hons) (Auckland) ------------------------:
: PhD Student, Computer Laboratory, University of Cambridge, England. :
: (and recently of the University of Glasgow, Scotland. [><] ) :
: Native of Antipodean Auckland, New Zealand: 174d47' E, 36d55' S. :
: http://www.cl.cam.ac.uk/users/kw217/ mailto:[EMAIL PROTECTED] :
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