Re: constraint deduction bug?

22 Mar 2013

      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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