Hi, On 20/01/12 01:02, Patrick Wheeler wrote: > ++ (if stdenv.isDarwin then stdenv.lib.optionals cupsSupport [ > cups ] else []); You can write this a bit cleaner as: stdenv.lib.optional (cupsSupport && !stdenv.isDarwin) cups -- Eelco Dolstra | http://www.st.ewi.tudelft.nl/~dolstra/