haskell-project.nix

# This template will give you a prompt with:
#    - ghc
#    - cabal
#    - ghc-mod
#    - the libraries: free, mtl, transformers
#
# to run: nix-shell haskell-project.nix
#
# to specify specific version of haskell, you can: 
#     nix-shell --arg haskellPackages 'with import <nixpkgs> {}; haskellPackages_ghc783_profiling'
# (I think) to specify a specific set of nixpkgs via nix channel
#     1. nix-channel --add http://nixos.org/channels/name my-new-nixos-channel
#     2. nix-channel --update
#     3. nix-shell --args nixpkgs 'import <my-new-nixos-channel> {}'

{ nixpkgs ? (import <nixpkgs> {})
, haskell ? (import <nixpkgs> {}).haskellPackages }:
let
  myEnvFun = nixpkgs.myEnvFun;
  cabalInstall = haskell.cabalInstall;
  free = haskell.free;
  ghc = haskell.ghc;
  ghcmod = haskell.ghcMod;
  mtl = haskell.mtl;
  transformers = haskell.transformers;
in rec {
  tmpEnv = myEnvFun {·
    name = "tmp-haskell-project-env";

    buildInputs = [
      # build tools
      cabalInstall
      ghc
      ghcmod
      
      # libs
      free
      mtl
      transformers
    ];
  };
}