[replace our Data.Utils.headM with Data.Maybe.listToMaybe
Helmut Grohne <grohne@cs.uni-bonn.de>**20140718124255
 Ignore-this: 5c5280d571982ca8e29449c27cdeaf22
] hunk ./src/Data/Util.hs 20
-printQ q = (runQ q) >>= putStrLn . pprint 
-showQ q = (runQ q) >>= putStrLn . show
-
-headM l = if null l then fail "empty list" else return . head $ l
+printQ :: (Ppr a, Show a) => Q a -> IO ()
+printQ q = runQ q >>= putStrLn . pprint
+showQ :: (Show a) => Q a -> IO ()
+showQ q = runQ q >>= putStrLn . show
hunk ./src/Igor2/RuleDevelopment/ListCata.hs 150
-    mkMapIO r = liftM (rule (init . lhs $ r)) (headM . subterms . rhs $  r)
-    
-                                         
+    mkMapIO r = liftM (rule (init . lhs $ r)) (listToMaybe . subterms . rhs $  r)
+
+