[Haskell-cafe] Fundeps and overlapping instances
anthony_clayden at clear.net.nz
Sun May 27 05:49:08 CEST 2012
Gábor Lehel <illissius <at> gmail.com> writes:
> On Fri, May 25, 2012 at 7:06 AM, AntC <anthony_clayden <at> clear.net.nz>
> > But it looks like the work SPJ pointed to is using closed style. ...
> If you're referring to the NewAxioms work Simon linked to in the other
> thread, I don't see it explicitly stated that all instances have to be
> within a single module. Especially section 3.3 (Translation) of the
> pdf seems to suggest otherwise. Though it also doesn't seem to be
> the same as what you're asking for. As far as I can tell, with
> NewAxioms, wherever you could currently have a type instance, you
> could instead have a type instance group. ... [snip]
Thanks Gábor, I think you could be right. (It needs some pretty close reading
of the equations.) I think in this case an example would be worth a thousand
typevars - double-barred of course.
I told them in Hebrew, I told them in Dutch,
I told them in Latin and Greek,
But I clear forgot (and it vexes me much),
That Haskell is what they speak.
The NewAxioms (draft) paper has a reference to Oleg's HList, but not his Type-
level Typeable, nor to Salzmann & Stuckey (2002), Chameleon, nor the myriad
discussions in the cafe and Haskell Prime.
It would be nice to see a statement along the lines of: we looked at X, Y and
Z, and didn't follow that approach because ...; or we believe that approach
can be incorporated like this ...
I thought it was a good research discipline to start with a literature survey,
to avoid re-inventing the wheel(?)
> It seems vaguely similar to a paper on instance chains
> I saw once.
Thanks, I saw that a while back but didn't look into it much at the time.
There's heaps of approaches out there to type-safe overlaps. Perhaps they're
all logically equivalent(?) So perhaps we're only bikeshedding about surface
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