clean up some ugly code

Utility/Data.hs

@@ -0,0 +1,17 @@
+{- utilities for simple data types
+ -
+ - Copyright 2013 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Utility.Data where
+
+{- First item in the list that is not Nothing. -}
+firstJust :: Eq a => [Maybe a] -> Maybe a
+firstJust ms = case dropWhile (== Nothing) ms of
+	[] -> Nothing
+	(md:_) -> md
+
+eitherToMaybe :: Either a b -> Maybe b
+eitherToMaybe = either (const Nothing) Just

Utility/Exception.hs

@@ -14,6 +14,7 @@ import qualified Control.Exception as E
 import Control.Applicative
 import Control.Monad
 import System.IO.Error (isDoesNotExistError)
+import Utility.Data
 
 {- Catches IO errors and returns a Bool -}
 catchBoolIO :: IO Bool -> IO Bool
@@ -54,5 +55,5 @@ tryNonAsync a = (Right <$> a) `catchNonAsync` (return . Left)
 
 {- Catches only DoesNotExist exceptions, and lets all others through. -}
 tryWhenExists :: IO a -> IO (Maybe a)
-tryWhenExists a = either (const Nothing) Just <$>
+tryWhenExists a = eitherToMaybe <$>
 	tryJust (guard . isDoesNotExistError) a

Utility/Misc.hs

@@ -91,12 +91,6 @@ massReplace vs = go [] vs
 			go (replacement:acc) vs (drop (length val) s)
 		| otherwise = go acc rest s
 
-{- First item in the list that is not Nothing. -}
-firstJust :: Eq a => [Maybe a] -> Maybe a
-firstJust ms = case dropWhile (== Nothing) ms of
-	[] -> Nothing
-	(md:_) -> md
-
 {- Given two orderings, returns the second if the first is EQ and returns
  - the first otherwise.
  -