{ pkgs ? (import <nixpkgs> {})
, compilerName ? "ghc801"
}:

rec {
  # haskellPackages = pkgs.haskell.packages."${compilerName}";
  haskellPackages = pkgs.haskell.packages."${compilerName}".override {
    overrides = self: super: {
      Shellac = pkgs.haskell.lib.appendPatch super.Shellac (pkgs.writeText "build.patch" ''
        From 20e394aa3ea287fcaacde9c076c9f49929b28ece Mon Sep 17 00:00:00 2001
        From: Gregor Kleen <gkleen@yggdrasil.li>
        Date: Sat, 11 Jun 2016 22:06:36 +0200
        Subject: [PATCH] Allow modification of state in beforePrompt

        ---
         src/System/Console/Shell/RunShell.hs | 6 ++++--
         1 file changed, 4 insertions(+), 2 deletions(-)

        diff --git a/src/System/Console/Shell/RunShell.hs b/src/System/Console/Shell/RunShell.hs
        index 79ffb54..3e0b95b 100644
        --- a/src/System/Console/Shell/RunShell.hs
        +++ b/src/System/Console/Shell/RunShell.hs
        @@ -217,9 +217,11 @@ shellLoop desc backend iss = loop
            bst = backendState iss
 
            loop st = do
        -        flushOutput backend bst
        +     flushOutput backend bst
        +     
        +     runSh st (outputString backend bst) (beforePrompt desc) >>= loop' . fst
 
        -        runSh st (outputString backend bst) (beforePrompt desc)
        +   loop' st = do
                 setAttemptedCompletionFunction backend bst
                  (completionFunction desc backend bst st)
 
        -- 
        2.8.3
      '');
    };
  };
  sequence = haskellPackages.callPackage ./sequence.nix {};
}