{ pkgs ? import <nixpkgs> {},
  system ? builtins.currentSystem }:

let inherit (pkgs) lib;
    releases = builtins.fromJSON (lib.strings.fileContents ./sources.json);
in lib.attrsets.mapAttrs (k: v: 
  if k == "master" then
    lib.attrsets.mapAttrs (k: v:
      (pkgs.stdenv.mkDerivation {
        pname = "zig";
        inherit (v.${system}) version;
        src = pkgs.fetchurl {
          inherit (v.${system}) url sha256;
        };
        dontConfigure = true;
        dontBuild = true;
        dontFixup = true;
        installPhase = ''
          mkdir -p $out/{doc,bin,lib}
          cp -r docs/* $out/doc
          cp -r lib/* $out/lib
          cp zig $out/bin/zig
        '';
      }))
      v
  else
    pkgs.stdenv.mkDerivation {
      pname = "zig";
      inherit (v.${system}) version;
      src = pkgs.fetchurl {
        inherit (v.${system}) url sha256;
      };
      dontConfigure = true;
      dontBuild = true;
      dontFixup = true;
      installPhase = ''
        mkdir -p $out/{doc,bin,lib}
        cp -r ${if k == "0.6.0" then "doc/*"
                else
                  if k == "0.7.0" then "langref.html"
                  else "docs/*"} $out/doc
        cp -r lib/* $out/lib
        cp zig $out/bin/zig
      '';
    })
  releases