the MPTC Dilemma (please solve)
sulzmann at comp.nus.edu.sg
Fri Mar 24 06:00:01 EST 2006
Manuel M T Chakravarty writes:
> > Another thing, here's an excerpt of the current summary of the MPTC
> > dilemma from
> > http://haskell.galois.com/cgi-bin/haskell-prime/trac.cgi/wiki
> > Multi Parameter Type Classes Dilemma ¦
> > Options for solving the dilemma ¦
> > 2. Put AssociatedTypes on the fast-track for sainthood
> > Associated Types ¦
> > Cons ¦
> > * Only a prototype implementation so far
> > This is a *inaccurate* and highly *misleading* summary.
> I didn't write that wiki page plus you are citing individual sentences
> out of a larger text.
This wasn't meant as a "personal attack". If you (or whoever wrote)
feel offended, I'm sorry.
(risking that I repeat myself here)
- When it comes to typing, FDs strictly subsume ATs.
(FDs = as defined in the FD-CHR paper)
FYI, the next Chameleon release will supports FDs and ATs,
ATs are internally represented via FD-CHRs.
- All the challenging inference problems encountered for FDs
also apply to ATs (see my previous emails)
- FD-CHRs describe improvement *and* instance, superclass rules.
It's really the subtle interaction between improvement and
instances that causes the problem.
I also would like to point that none of the FD-CHR
results are "recent". The FD-CHR paper was published in ESOP'04,
that was two years ago. Since April 2004, there's an extended
version available as a TR. Correct, a revised version will somewhen
soon appear as a JFP paper.
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