anchor.diff: -{ lib, stdenv, fetchurl, fetchFromGitHub
  -, assembleReductionMatrix ? false
  +{ lib, stdenv, fetchFromGitHub
   , useCoefficients ? false
   , indicateProgress ? false
   , useGoogleHashmap ? false, sparsehash ? null
  
positive.code:   src = fetchFromGitHub {
      owner = "Ripser";
      repo = "ripser";
      rev = "f69c6af6ca6883dd518c48faf41cf8901c379598";
      sha256 = "1mw2898s7l29hgajsaf75bs9bjn2sn4g2mvmh41a602jpwp9r0rz";
    };
  
    #Patch from dev branch to make compilation work.
    #Will be removed when it gets merged into master.
    patches = [(fetchurl {
      url = "https://github.com/Ripser/ripser/commit/dc78d8ce73ee35f3828f0aad67a4e53620277ebf.patch";
      sha256 = "1y93aqpqz8fm1cxxrf90dhh67im3ndkr8dnxgbw5y96296n4r924";
    })];
  
    buildInputs = optional useGoogleHashmap sparsehash;
  
    buildFlags = [
      "-std=c++11"
      "-Ofast"
      "-D NDEBUG"
    ]
    ++ optional assembleReductionMatrix "-D ASSEMBLE_REDUCTION_MATRIX"
    ++ optional useCoefficients "-D USE_COEFFICIENTS"
    ++ optional indicateProgress "-D INDICATE_PROGRESS"
    ++ optional useGoogleHashmap "-D USE_GOOGLE_HASHMAP"
  
negative.code: 
  let
    inherit (lib) optional;
    version = "1.2.1";
  in
  stdenv.mkDerivation {
    pname = "ripser";
  