Alex Ferguson wrote:
>
> Kevin Atkinson:
>
> > I have a generic mutable array class which has a few basic methods:
> >
> > class MArray ... where
> > newArray :: Int -> m (mutArray st el)
> > write :: mutArray st el -> Int -> el -> m ()
> > read :: mutArray st el -> Int -> m el
> > freeze :: m mutArray st el -> m array el
> > thaw :: m array el -> m mutArray st el
> >
> > and it turns out that it is possible to create a full fledge
> > non-mutable array based on the mutable array class with the help of
> > this method:
> >
> > thawRunFreeze :: Array el
> > -> (m mutArray st el -> m ())
> > -> Array el
> >
> > Which will, as the signature suggests and name suggest, thaw an array,
> > perform some actions on the mutable array, and then freeze it,
> > returning the new array.
> >
> > The only problem is that it is impossible to have a generic
> > thawRunFreeze method in Haskell. So I had to resort to some ugly code
> > generation.
>
> Thanks for the example. If I understand you here, what you intend is
> not that there always _should_ be a thawRunFreeze, for any type, but
> that it should be possible to have an implemention, or semi-generic
> hierarchy of implementations, of this which either uses or doesn't use
> such a method, as appropriate/available.
>
> I think this is certainly do-able, and I've seen it addressed, if
> not necessarily entirely unqualifiedly solved, in a couple of papers.
> If this is your main concern about the flexibility of Haskell types,
> then be of good cheer as I'm certain this one is soluble, entirely
> within the basic 'look and feel' of Haskell typing.
>
> Which isn't to say that I'm not handwaving over a morass of technical
> details, or expecting the language committee to agree on any such things
> within the netx language revision or three. ;-)
If you are so convinced than do it. Sense a solution to MTC should be
in Hugs soon I don't wish to pursue this any farther until I get a copy
of Hugs with Mark's solution so that I can play with it some. From his
web site his solution looks very promising.
--
Kevin Atkinson
[EMAIL PROTECTED]
http://metalab.unc.edu/kevina/
