/* Get the path to the main program of a derivation with either
     meta.mainProgram or pname or name

     Type: getExe :: derivation -> string

     Example:
       getExe pkgs.hello
       => "/nix/store/g124820p9hlv4lj8qplzxw1c44dxaw1k-hello-2.12/bin/hello"
       getExe pkgs.mustache-go
       => "/nix/store/am9ml4f4ywvivxnkiaqwr0hyxka1xjsf-mustache-go-1.3.0/bin/mustache"
  */
  getExe = x:
    "${lib.getBin x}/bin/${x.meta.mainProgram or (lib.getName x)}";

  /* This function takes an argument that's either a derivation or a
     derivation's "name" attribute and extracts the name part from that
     argument.

     Example:
       getName "youtube-dl-2016.01.01"
       => "youtube-dl"
       getName pkgs.youtube-dl
       => "youtube-dl"
  */
  getName = x:
   let
     parse = drv: (parseDrvName drv).name;
   in if isString x
      then parse x
      else x.pname or (parse x.name);