anchor.diff:          installPhase = "ln -s $src $out";
         };
   
  +    "exists" = pkgs.stdenv.mkDerivation {
  +        name = "exists";
  +        version = "v4.0.0";
  +        src = pkgs.fetchgit {
  +          url = "https://github.com/purescript/purescript-exists.git";
  +          rev = "ef53359aebc09bf863800ca86ad1dcd76f0b08ae";
  +          sha256 = "0bbdbw3jaqyi8dj2d52zvfgx4vl84d8cr6hp43vy8lfjfcbj0wlk";
  +        };
  +        phases = "installPhase";
  +        installPhase = "ln -s $src $out";
  +      };
  +
       "filterable" = pkgs.stdenv.mkDerivation {
           name = "filterable";
           version = "v3.0.1";
  
positive.code:         installPhase = "ln -s $src $out";
        };
  
      "record-format" = pkgs.stdenv.mkDerivation {
          name = "record-format";
          version = "v1.0.0";
          src = pkgs.fetchgit {
            url = "https://github.com/kcsongor/purescript-record-format.git";
            rev = "657afb6f2ec81610b8008ffcc1386e6d1bf7141a";
            sha256 = "1ddr73lrccj24iz1gbdzaipibdklcwmm88dhn0p2jjsm47mmkjzv";
          };
          phases = "installPhase";
          installPhase = "ln -s $src $out";
        };
  
      "refs" = pkgs.stdenv.mkDerivation {
          name = "refs";
          version = "v4.1.0";
  
negative.code:         installPhase = "ln -s $src $out";
        };
  
      "simple-json" = pkgs.stdenv.mkDerivation {
          name = "simple-json";
          version = "v7.0.0";
  