Add a comment about when maybePrefixMatch can be removed

[ghc-hetmet.git] / compiler / utils / Util.lhs

diff --git a/compiler/utils/Util.lhs b/compiler/utils/Util.lhs
index 8473faf..495df82 100644 (file)
--- a/compiler/utils/Util.lhs
+++ b/compiler/utils/Util.lhs
@@ -79,9 +79,12 @@ module Util (
 
 #include "HsVersions.h"
 
-import Panic           ( panic, trace )
 import FastTypes
 
+#ifdef DEBUG
+import Panic           ( panic, trace )
+#endif
+
 import Control.Exception ( Exception(..), finally, catchDyn, throw )
 import qualified Control.Exception as Exception
 import Data.Dynamic    ( Typeable )
@@ -89,10 +92,11 @@ import Data.IORef   ( IORef, newIORef )
 import System.IO.Unsafe        ( unsafePerformIO )
 import Data.IORef      ( readIORef, writeIORef )
 
-import qualified Data.List as List ( elem, notElem )
-
+import qualified Data.List as List ( elem )
 #ifndef DEBUG
 import Data.List               ( zipWith4 )
+#else
+import qualified Data.List as List ( notElem )
 #endif
 
 import Control.Monad   ( when )
@@ -586,6 +590,8 @@ cmpList cmp (a:as) (b:bs)
 \end{code}
 
 \begin{code}
+-- This (with a more general type) is Data.List.stripPrefix from GHC 6.8.
+-- This definition can be removed once we require at least 6.8 to build.
 maybePrefixMatch :: String -> String -> Maybe String
 maybePrefixMatch []    rest = Just rest
 maybePrefixMatch (_:_) []   = Nothing