qforeign-0.62

[Manuel M. T. Chakravarty]

qrczak at knm.org.pl (Marcin 'Qrczak' Kowalczyk) wrote,

> Fri, 01 Dec 2000 13:10:43 +1100, Manuel M. T. Chakravarty <chak at cse.unsw.edu.au> pisze:
> 
> > Instead of the 
> > 
> >   newtype Window = Window ForeignObj
> > 
> > way of wrapping foreign ADTs that we used so far, should we
> > use
> > 
> >   newtype WindowTag = WindowTag ()
> >   type    Window    = ForeignObj WindowTag
> > 
> > ?
> 
> This exposes the fact that Window is a ForeignObj. Ok, but maybe some
> people want it to be more abstract - clients need not to know that
> it's just a ForeignObj. Such type is usually exported.

I don't want to exclude that you write

  newtype WindowTag = WindowTag ()
  newtype Window    = ForeignObj WindowTag

That's fine, too.  It would still make 

  withForeignPtr :: ForeignObj a -> (Ptr a -> IO b) -> IO b

nicer, because it constrains the parameter of `Ptr'.

> BTW, IMHO it's more natural to write
>     data WindowTag = WindowTag
> and it would be yet more natural (and would avoid ghc's warning about
> a constructor which is never used) if we were allowed to write
>     data WindowTag
> to create a void type.

I agree, but that would be an extension to Haskell and so is
not an option right now.  We have to work with what we got.

Cheers,
Manuel