[nix@nixos:~/myproj]$ cat nix/stack-shell.nix
{ghc}:

let
  nixpkgs = import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/50a5d4c77307e7da226294f924098d98d5c38990.tar.gz") {};
in
nixpkgs.haskell.lib.buildStackProject {
  inherit ghc;
  name = "myEnv";
  buildInputs = with nixpkgs.pkgs; [ lzma glpk pcre postgresql zlib git ];
}

[nix@nixos:~/myproj]$ stack build --nix
error: attribute 'ghc8103' missing, at (string):1:29
(use '--show-trace' to show detailed location information)

[nix@nixos:~/myproj]$ nix-instantiate  -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/50a5d4c77307e7da226294f924098d98d5c38990.tar.gz --eval -E "with (import <nixpkgs> {}); lib.attrNames haskell.compiler"
[ "ghc8101" "ghc8102" "ghc8102Binary" "ghc8102BinaryMinimal" "ghc8103" "ghc822Binary" "ghc865" "ghc865Binary" "ghc882" "ghc883" "ghc884" "ghc901" "ghcHEAD" "ghcjs" "ghcjs86" "integer-simple" "native-bignum" ]