[Haskell-cafe] Re: MPTCs and rigid variables

mm schneegloeckchen at gmx.li
Wed Mar 7 10:10:09 EST 2007

F, FD, FC, AT, SPJ ;) WTH does it mean?

On Wed, Mar 07, 2007 at 10:12:11AM +0100, apfelmus at quantentunnel.de wrote:
> Claus Reinke wrote:
> >>> ps. i was somewhat shocked to read that SPJ wants FDs gone.
> >>
> >> Why?  Simon has good taste. :)
> > 
> > de gustibus non est disputandum ;)
> > 
> > FD have uses and problems and AT have uses and problems. starting anew
> > with the latter doesn't fix the problems, it just changes their form.
> Well, the choice between FD and AT (and maybe yet undiscovered
> alternatives) is entirely a matter of "convenience" as much as
> everything related to type inference is. The same goes for type classes
> or subtyping: all these can be translated to system F (or FC for FD and
> AT) so they don't add abstraction power at run-time. Their only but
> important purpose is to auto-infer code.
> FD are pretty much type-level programming in a kind of mini-prolog. Of
> course, AT are type-level programming as well, but functional in style,
> which is arguably more compelling for a functional base language. At
> least, I think that FD are somehow ugly.
> > in particular, many of the problems with FD are ambiguities in
> > interpreting interactions with other popular features, such as overlap
> > resolution. it took half a decade of practical experience to expose
> > such issues for FD, and i don't see the fact that AT haven't reached
> > that stage yet as any advantage.
> Quite telling that it took half a decade to shed light on the semantics
> of the many FD variants, isn't it? :)
> I guess that AT will come with semantics included because it's otherwise
> unclear how to implement them. Implementing FD is simply easier as type
> inference already is a kind of mini-prolog. Of course, that doesn't
> simplify their semantics at all. In a sense, knowing AT is knowing how
> much functional in style type inference can be.
> Regards,
> apfelmus
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