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@haskell.org [mailto:ghc-devs- bounces@haskell.org] On Behalf Of Richard Eisenberg Sent: Friday, March 22, 2013 1:11 AM To: Gabor Greif Cc: ghc-devs@haskell.org Subject: Re: constraint deduction bug?

It certainly looks trivial to me.

Richard

On Mar 21, 2013, at 7:59 PM, Gabor Greif 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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http://hackage.haskell.org/trac/ghc/ticket/7786 Thanks for responding! Cheers, Gabor On 3/22/13, Dimitrios Vytiniotis 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@haskell.org [mailto:ghc-devs- bounces@haskell.org] On Behalf Of Richard Eisenberg Sent: Friday, March 22, 2013 1:11 AM To: Gabor Greif Cc: ghc-devs@haskell.org Subject: Re: constraint deduction bug?

It certainly looks trivial to me.

Richard

On Mar 21, 2013, at 7:59 PM, Gabor Greif 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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