anchor.diff:    silent = mkDerivation {
       name = "silent";
       buildCommand = ''
  +      touch $out
         sleep 60
       '';
     };
  
positive.code:   closeLog = mkDerivation {
      name = "silent";
      buildCommand = ''
        exec > /dev/null 2>&1
        sleep 1000000000
      '';
  
negative.code:   infiniteLoop = mkDerivation {
      name = "timeout";
      buildCommand = ''
        touch $out
        echo "‘timeout’ builder entering an infinite loop"
        while true ; do echo -n .; done
      '';
  