anchor.diff:    src = fetchFromGitHub {
       owner = "coq";
       repo = "bignums";
  -    inherit rev sha256;
  +    inherit (param) rev sha256;
     };
   
     buildInputs = [ coq.ocaml coq.camlp5 coq.findlib coq ];
  
positive.code: { stdenv, fetchFromGitHub, coq }:
  
  let rev_and_sha = {
    "8.6" = {
      rev = "v8.6.0";
      sha256 = "0553pcsy21cyhmns6k9qggzb67az8kl31d0lwlnz08bsqswigzrj";
    };
    "8.7" = {
      rev = "V8.7.0";
      sha256 = "11c4sdmpd3l6jjl4v6k213z9fhrmmm1xnly3zmzam1wrrdif4ghl";
    };
  };
  in
  
  if ! (rev_and_sha ? "${coq.coq-version}") then
    throw "bignums is not available for Coq ${coq.coq-version}"
  else with rev_and_sha."${coq.coq-version}";
  
  stdenv.mkDerivation rec {
  
  
negative.code:     platforms = coq.meta.platforms;
    };
  
    passthru = {
      compatibleCoqVersions = v: builtins.elem v [ "8.6" "8.7" ];
    };
  }
  