disable doctests conditionally

test/doctest.hs

@@ -1,10 +1,16 @@
-{-# LANGUAGE DoAndIfThenElse #-}
 module Main where
 
+#ifndef GYEHOEK_NO_DOCTEST
 import Test.DocTest (mainFromCabal)
-import System.Environment (getArgs, lookupEnv)
+#endif
+import System.Environment (getArgs)
 import System.IO (stderr, hPutStrLn)
 
 
 main :: IO ()
-main = mainFromCabal "gyehoek" =<< getArgs
+main =
+#ifndef GYEHOEK_NO_DOCTEST
+  mainFromCabal "gyehoek" =<< getArgs
+#else
+  hPutStrLn stderr "skipping doctests due to broken nix environment."
+#endif