[Nix-dev] Using several versions of GHC at once

[Vladimír Čunát]

On 06/15/2013 10:06 PM, Nikita Karetnikov wrote:
>> Priorities can be assigned in the sources.
>
> Could you show an example?  It seems these files [1,2] don't have any.
>
> [1] https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/libraries/haskell/binary/0.6.0.0.nix
> [2] https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/compilers/ghc/6.10.1.nix

Hmm, especially haskell packages are IMO better specified directly by 
attribute. This also always gives only one possibility and it's faster. 
Default attributes are here [1,2]. Here no priorities seem to be used, 
so the highest version should be chosen among them (I see no duplicities 
in these cases).

For example in [3] there's a bunch of sqlite versions with lowered 
priorities.

[1] 
https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/haskell-packages.nix#L590
[2] 
https://github.com/NixOS/nixpkgs/blob/master/pkgs/top-level/all-packages.nix#L2528
[3] 
https://github.com/NixOS/nixpkgs/blob/x-updates/pkgs/top-level/all-packages.nix#L5178


Vlada


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