Class System current status
Manuel M T Chakravarty
chak at cse.unsw.edu.au
Mon May 15 17:19:46 EDT 2006
> Haskell' should define a standard language for use TODAY--and it
> should be 100% clear what that language is, with no pussy-footing
> around difficult choices. In my view it should include FDs. Then in
> the future they may be replaced--but it should then be clear that this
> IS a replacement, with no arguments of the sort "well it's not really
> an incompatible change because FDs were only in an appendix"! Let's
> face it, people ARE going to use FDs whatever the standard says,
> because they're just so godamn useful, and rewriting those programs if
> FDs are replaced by ATs is not going to be any easier because it's an
> appendix that's changing, rather than the main body of the report.
I agree that having FDs in the appendix does not make an essential
difference to how easy they are to replace. Hence, I proposed a
variation on this proposal is that we actually delay issuing the
appendix. More precisely,
* Specify MPTCs in the main language.
* Finalise Haskell' without an FD/AT appendix.
* Take our time to find out exactly how we want to do type level
programming (with FDs, or ATs, or both). Once we know, we add an
appendix on type-level programming.
This moves the MPTC dilemma out of the critical path for Haskell' as a
whole, but avoids that we have to rush the FD/AT issue.
PS: I actually thought that this was what Simon proposed when he
originally brought up the appendix idea, which may have been only
between the class system subcommittee members.
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