MPTCs and functional dependencies

isaac jones ijones at
Tue Mar 28 13:26:31 EST 2006

On Tue, 2006-03-28 at 14:32 +0100, Simon Peyton-Jones wrote:
> My current take, FWIW.
> * MPTCs are very useful.  They came along very rapidly (well before
> H98).  I think we must put them in H'
> * But MPTCs are hamstrung without FDs or ATs
> * FDs and ATs are of the same order of technical difficulty, as Martin
> says
> * ATs are (I believe) a bit weaker from the expressiveness point of view
> (zip example), but are (I believe) nicer to program with.  
> * BUT we have way more experience with actually programming with FDs.
> ATs fail the "well-established" test by a mile.
> * Largely due to Martin's work, we now have a much better handle on just
> what restrictions on FDs make type inference tractable.  So I believe
> there is a solid MPTC+FD story that we could embody in H'.
> * Medium term, I think ATs may *at the programming-language level*
> displace FDs, because they are nicer to program with.  But that's just
> my opinion, and we don't have enough experience to know one way or the
> other.

This analysis is similar to what I have here:

Could someone flesh out the wiki w/ Simon's data and links to the new
information from Martin?



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