quicc install haskell stacc for epitecc

cmds.sh

# install nix
# logout then login
# add said file to ~/.config/nixpkgs/overlays/haskell.nix
# NOT NEEDED ANYMORE: add `{ allowBroken = true; }` to ~/.config/nixpkgs/config.nix
nix-channel --list
## should _NOT_ have nixpkgs-unstable in output, else do
nix-channel --add https://nixos.org/channels/nixpkgs nixpkgs
# install pkgset
nix-env -iA nixpkgs.haskellPkgs
# any other time to clear all other packages and update
nix-env-hs

haskell.nix

self: super:

let
  unstable = import (fetchTarball "channel:nixpkgs-unstable") { inherit (self) config; };
in
{
  haskellPkgs = ( super.haskellPkgs or {} ) // {

    nix-env-hs = super.writeScriptBin "nix-env-hs" ''
      #!${super.stdenv.shell}
      if ! command -v nix-env &>/dev/null; then
          echo "warning: nix-env was not found in PATH, add nix to userPackages" >&2
          PATH=${self.nix}/bin:$PATH
      fi
      PENV=(
        haskellPkgs
      )
      exec nix-env -f '<nixpkgs>' -r -iA \
            ''${PENV[@]} \
            "$@"
    '';

    env = self.haskellPackages.ghcWithHoogle (ps: with ps; [
      hasktags
      stylish-haskell
      async
      bytestring
      filepath
      mtl
      text
    ]);
    inherit (self) hlint cabal-install cabal2nix stack;
    inherit (unstable.haskellPackages) implicit-hie haskell-language-server;
  };
}