{ mkDerivation, base, fetchurl, numtype-dk }:
mkDerivation {
  pname = "exact-pi";
  version = "0.4.1.2";
  src = fetchurl {
    url = "http://example.org/";
    sha256 = "abc";
  };
  libraryHaskellDepends = [ base numtype-dk ];
  homepage = "https://github.com/dmcclean/exact-pi/";
  description = "Exact rational multiples of pi (and integer powers of pi)";
  license = stdenv.lib.licenses.mit;
}