copy JGM's utf8 IO module from pandoc

hledger-lib/Hledger/Data/UTF8.hs

@@ -0,0 +1,75 @@
+{-
+Copied from pandoc.
+
+----------------------------------------------------------------------
+Copyright (C) 2010 John MacFarlane <jgm@berkeley.edu>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+-}
+
+{- |
+   Module      : Text.Pandoc.UTF8
+   Copyright   : Copyright (C) 2010 John MacFarlane
+   License     : GNU GPL, version 2 or above 
+
+   Maintainer  : John MacFarlane <jgm@berkeley.edu>
+   Stability   : alpha
+   Portability : portable
+
+UTF-8 aware string IO functions that will work with GHC 6.10 or 6.12.
+-}
+module Hledger.Data.UTF8 ( readFile
+                         , writeFile
+                         , getContents
+                         , putStr
+                         , putStrLn
+                         , hPutStr
+                         , hPutStrLn
+                         )
+
+where
+import qualified Data.ByteString.Lazy as B
+import Data.ByteString.Lazy.UTF8 (toString, fromString)
+import Prelude hiding (readFile, writeFile, getContents, putStr, putStrLn)
+import System.IO (Handle)
+import Control.Monad (liftM)
+
+bom :: B.ByteString
+bom = B.pack [0xEF, 0xBB, 0xBF]
+
+stripBOM :: B.ByteString -> B.ByteString
+stripBOM s | bom `B.isPrefixOf` s = B.drop 3 s
+stripBOM s = s
+
+readFile :: FilePath -> IO String
+readFile = liftM (toString . stripBOM) . B.readFile
+
+writeFile :: FilePath -> String -> IO ()
+writeFile f = B.writeFile f . fromString
+
+getContents :: IO String
+getContents = liftM (toString . stripBOM) B.getContents
+
+putStr :: String -> IO ()
+putStr = B.putStr . fromString
+
+putStrLn :: String -> IO ()
+putStrLn = B.putStrLn . fromString
+
+hPutStr :: Handle -> String -> IO ()
+hPutStr h = B.hPutStr h . fromString
+
+hPutStrLn :: Handle -> String -> IO ()
+hPutStrLn h s = hPutStr h (s ++ "\n")