[Nix-dev] Haskell dependencies in a project

[Brian McKenna]

You need to call pkgs.haskellPackages.callPackage on my-dep, so it
will look something like:

    dependencies = with pkgs.haskellPackages; [
      aeson (callpackage my-dep { })
    ];

It's also possible to use the 'override' attribute instead, which
would be useful if you later add a dependency which uses my-dep:

https://nixos.org/nixpkgs/manual/#how-to-build-projects-that-depend-on-each-other

On 3 April 2016 at 12:15, Tomasz Czyż <tomasz.czyz at gmail.com> wrote:
> Hi,
>
> I'm trying to make a nix/haskell package (with executable) with some
> dependencies (from nixpkgs and some locally declared).
>
> I have my-dep directory with haskell package exposing library and src
> directory which contains application using my-dep dependency and aeson
> package from nixpkgs.
>
> Here is my nix expression:
>
> { pkgs ? import <nixpkgs> {} }:
> let
>   my-dep = pkgs.haskellPackages.mkDerivation {
>     pname = "my-dep";
>     version = "0.1.0.0";
>     src = ./my-dep;
>     isLibrary=true;
>     isExecutable=false;
>     license = with pkgs; stdenv.lib.licenses.unfree;
>     doHaddock=false;
>   };
>   dependencies = with pkgs.haskellPackages; [
>     aeson my-dep
>   ];
>   ghc = pkgs.haskellPackages.ghcWithPackages(hs:(dependencies));
> in
> pkgs.haskellPackages.mkDerivation {
>   pname = "haskell-project";
>   version = "0.1.0.0";
>   src = ./src;
>   isLibrary = false;
>   isExecutable = true;
>   buildTools = [ghc];
>   buildDepends = dependencies;
>   license = with pkgs; stdenv.lib.licenses.unfree;
> }
>
> (library expose 1 function which print text and main project just imports
> aeson and my-dep and uses function from library)
>
> When building it, I am getting error:
>
> --------------------------------
> Building haskell-project-0.1.0.0...
> Preprocessing executable 'haskell-project' for haskell-project-0.1.0.0...
>
> Main.hs:2:18:
>     Could not find module ‘MyDep’
>     Use -v to see a list of the files searched for.
> builder for
> ‘/nix/store/43lbwp4qfigjwkf97nqp4h21hsrf5yr2-haskell-project-0.1.0.0.drv’
> failed with exit code 1
> error: build of
> ‘/nix/store/43lbwp4qfigjwkf97nqp4h21hsrf5yr2-haskell-project-0.1.0.0.drv’
> failed
> ------------------------------------
>
> There is no problem with aeson (it's complaining about aeson when I remove
> dependency from nix expression), but there is a problem with my-dep
> dependency.
>
> Question is, how I should declare dependency for my-dep to make it working,
> to make haskell-project to use that dependency correctly?
>
> (if I run nix-shell with this expression I have the same error, but if I
> "cd" to my-dep directory and run ghc ../src/Main.hs it's working, it looks
> like ghs tries search for MyDep.hs only in current directory instead of
> package directory).
>
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