constraint deduction bug?

[Simon Peyton-Jones]

Yes, looks odd. Please do give us a test case.  Thank you!

S

| -----Original Message-----
| From: ghc-devs-bounces at haskell.org [mailto:ghc-devs-bounces at haskell.org]
| On Behalf Of Dimitrios Vytiniotis
| Sent: 22 March 2013 10:01
| To: Richard Eisenberg; Gabor Greif
| Cc: ghc-devs at haskell.org
| Subject: RE: constraint deduction bug?
| 
| Is Intersect (or some other of the constructors involved, maybe Empty?)
| kind-polymorphic and instantiated in the two sites (wanted vs. given)
| with different kind variables which end up being unconstrained, or
| something like that? Then it might be the case that we don't get a match
| (which is rather unintuitive, I
| agree) and the constraint is not solved.
| 
| Even if it's a case like this it's probably best to do submit a small
| reproducible example and we will have a look.
| 
| Thanks
| d-
| 
| 
| 
| > -----Original Message-----
| > From: ghc-devs-bounces at haskell.org [mailto:ghc-devs-
| > bounces at haskell.org] On Behalf Of Richard Eisenberg
| > Sent: Friday, March 22, 2013 1:11 AM
| > To: Gabor Greif
| > Cc: ghc-devs at haskell.org
| > Subject: Re: constraint deduction bug?
| >
| > It certainly looks trivial to me.
| >
| > Richard
| >
| > On Mar 21, 2013, at 7:59 PM, Gabor Greif <ggreif at gmail.com> wrote:
| >
| > > In context of a bigger source file I got this error from GHC (HEAD)
| > >
| > >    Could not deduce (Intersect
| > >                        [KeySegment] (BuriedUnder sub k ('Empty
| > > [KeySegment])) inv
| > >                      ~ 'Empty [KeySegment])
| > >    from the context (Intersect
| > >                        [KeySegment] (BuriedUnder sub k ('Empty
| > > [KeySegment])) inv
| > >                      ~ 'Empty [KeySegment])
| > >      bound by a pattern with constructor
| > >                 Nil :: forall (k :: BOX). Sing (Inventory k) ('Empty
| k),
| > >               in a pattern binding in
| > >                    'do' block
| > >
| > > Can somebody confirm that this constraint should be trivially
| > > deducible from the context?
| > >
| > > Then I'll try to come up with a reduced repro case.
| > >
| > > Cheers,
| > >
| > > 	Gabor
| > >
| > > _______________________________________________
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| >
| >
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