constraint deduction bug?

[Gabor Greif]

http://hackage.haskell.org/trac/ghc/ticket/7786

Thanks for responding!

Cheers,

    Gabor

On 3/22/13, Dimitrios Vytiniotis <dimitris at microsoft.com> wrote:
> 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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