X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FList.hs;h=061ad42a01ad19d3b7b2f1498b03497946410db4;hb=41e8fba828acbae1751628af50849f5352b27873;hp=221a340a24cb55daa7d34b27d83fbc2a936b6cff;hpb=2b17b2a58087c438ebd5a7de91b2e9f69e09a17f;p=ghc-base.git

diff --git a/Data/List.hs b/Data/List.hs
index 221a340..061ad42 100644
--- a/Data/List.hs
+++ b/Data/List.hs
@@ -1,4 +1,5 @@
-{-# OPTIONS_GHC -XNoImplicitPrelude #-}
+{-# LANGUAGE CPP, NoImplicitPrelude, MagicHash #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.List
@@ -1038,10 +1039,23 @@ product l       = prod l 1
 -- characters.  The resulting strings do not contain newlines.
 lines                   :: String -> [String]
 lines ""                =  []
+#ifdef __GLASGOW_HASKELL__
+-- Somehow GHC doesn't detect the selector thunks in the below code,
+-- so s' keeps a reference to the first line via the pair and we have
+-- a space leak (cf. #4334).
+-- So we need to make GHC see the selector thunks with a trick.
+lines s                 =  cons (case break (== '\n') s of
+                                    (l, s') -> (l, case s' of
+                                                    []      -> []
+                                                    _:s''   -> lines s''))
+  where
+    cons ~(h, t)        =  h : t
+#else
 lines s                 =  let (l, s') = break (== '\n') s
                            in  l : case s' of
                                         []      -> []
                                         (_:s'') -> lines s''
+#endif
 
 -- | 'unlines' is an inverse operation to 'lines'.
 -- It joins lines, after appending a terminating newline to each.