Jacques Carette wrote:
I tried to see the discussion that led to class aliases being rejected
as a proposal, but could not find links on the Wiki. In fact, in Trac
(#101) that proposal is still a 'maybe', but with no updates. Is there
a competing proposal that got accepted?
[Without a mechanism like class aliases, breaking up Num into a
hierarchy of proper mathematical concepts becomes too unwieldly to be
realistic. This is a real stumbling block for anyone trying to use the
class system to encode fine-grained mathematical concepts.]
We want to get Haskell' done, and unfortunately that may mean rejecting
some good proposals - in this case, class aliases is a fairly large
feature that we don't have enough experience with yet, so it was dropped
(I proposed dropping it recently to the committee, and no-one argued
against).
That's not to say it isn't worthwhile, and this certainly doesn't
prevent it from being adopted in a future version of the standard. We'd
like to see it implemented in GHC, too.
BTW, by the end of this process I do want to make sure we've documented
the rationale for all the decisions, so that future committees have a
useful knowledge base to work from.
Cheers,
Simon
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