GF/src is now for 2.9, and the new sources are in src-3.0 - keep it this way until the release of GF 3

src-3.0/GF/Data/SharedString.hs

@@ -0,0 +1,19 @@
+
+module GF.Data.SharedString (shareString) where
+
+import Data.HashTable as H
+import System.IO.Unsafe (unsafePerformIO)
+
+{-# NOINLINE stringPool #-}
+stringPool :: HashTable String String
+stringPool = unsafePerformIO $ new (==) hashString
+
+{-# NOINLINE shareString #-}
+shareString :: String -> String
+shareString s = unsafePerformIO $ do
+    mv <- H.lookup stringPool s
+    case mv of
+	    Just s' -> return s'
+	    Nothing -> do
+		       H.insert stringPool s s
+		       return s