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From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: [PATCH] gnu: mesa: Add libva input.
Date: Fri, 01 May 2015 00:17:21 +0200
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In-Reply-To: <87oam6c9ja.fsf@taylan.uni.cx> ("Taylan Ulrich
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To: Taylan Ulrich =?utf-8?Q?=22Bay=C4=B1rl=C4=B1?=
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Cc: guix-devel@gnu.org

taylanbayirli@gmail.com (Taylan Ulrich "Bay=C4=B1rl=C4=B1/Kammer") skribis:

> Actually, I hit the problem again now; it's during the compilation of
> .scm files.
>
> The problem seems to be that 'inherit' fields of packages are evaluated
> eagerly, so when video.scm directly or indirectly imports gl.scm before
> having bound the libva variable to its value, and the libva-without-mesa
> definition in gl.scm tries to reference libva, it errors.
>
> I can solve this by wrapping the libva-without-mesa definition in a
> delay, and forcing it in the input field of mesa.  Is that OK?

Yes, indeed, the solution in such cases is to use a promise or a thunk,
or to have the two definitions in the same file.

Thanks,
Ludo=E2=80=99.