[Nix-dev] nix-shell for a custom haskell library

[Peter Jones]

Dmitry Malikov <malikov.d.y at gmail.com> writes:
> I'm trying to setup a development environment for a custom haskell library
> basing on a tutorial by Oliver Charles
> (http://wiki.ocharles.org.uk/Nix).

FWIW I've been playing with Nix and Haskell a lot lately trying to come
up with the perfect development environment.  This is what I have so
far.  Everything below is done with a recent copy of nixpkgs.

I have a shell function called nix-hs-build that does the following:

    # Create a default.nix for the Haskell project in $PWD:
    nix-shell -p haskellPackages.cabal2nix \
      --command "cabal2nix $PWD $@ > default.nix"

    # Build the project:
    nix-hs-shell --command  $(which hsbuild.sh) "$@"

The contents of hsbuild.sh can be found here:

  https://gist.github.com/pjones/7a6023d3567ff2ed49bf

The `nix-hs-shell` command is another shell function that just runs
nix-shell with cabal-install and hlint in the environment so that
hsbuild.sh can work.  Here are the details:

    function nix-hs-shell () {
      override=~/.nixpkgs/envs/dev/haskell-cabal.nix
      nix-shell -I pwd=$PWD --pure "$@" $override
    }


Where haskell-cabal.nix contains:

    { nixpkgs  ? import <nixpkgs> {}
    , compiler ? "ghc7101"
    }:
    
    let
      pkgs = nixpkgs.pkgs;
      ghc  = pkgs.haskell.packages.${compiler};
      f    = import <pwd>;
      drv  = ghc.callPackage f {};
    in
      (pkgs.haskell.lib.addBuildTools drv [
        ghc.cabal-install
        ghc.hlint
      ]).env

With those pieces I can just run `nix-hs-build` without having to create
any sort of *.nix file by hand.  If I change the project's cabal file
and run `nix-hs-build` it will work since it generates the default.nix
again.  I can also change compilers with a flag:

    nix-hs-build --compiler ghc784

> How to get Network.EngineIO available inside a nix-shell in this case?

Using my setup above, the library would be installed in ./dist

-- 
Peter Jones, Founder, Devalot.com
Defending the honor of good code

-- 
Peter Jones, Founder, Devalot.com
Defending the honor of good code