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Add Data.Text.Foreign

--HG--
extra : convert_revision : 02c86e14ab74bed2e8f3d0088713c6d029f40675
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commit 749282a3322a7616545a98058e403abba7176591 1 parent e5250f0
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  1. +89 −0 Data/Text/Foreign.hs
  2. +1 −0  text.cabal
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89 Data/Text/Foreign.hs
@@ -0,0 +1,89 @@
+{-# LANGUAGE BangPatterns #-}
+-- |
+-- Module : Data.Text.Foreign
+-- Copyright : (c) Bryan O'Sullivan 2009
+--
+-- License : BSD-style
+-- Maintainer : rtharper@aftereternity.co.uk, bos@serpentine.com,
+-- duncan@haskell.org
+-- Stability : experimental
+-- Portability : GHC
+--
+-- Support for using 'Text' data with native code via the Haskell
+-- foreign function interface.
+
+module Data.Text.Foreign
+ (
+ -- * Interoperability with native code
+ -- $interop
+
+ -- * Safe conversion functions
+ fromPtr
+ , useAsPtr
+ -- * Unsafe conversion code
+ , lengthWord16
+ , unsafeCopyToPtr
+ ) where
+
+import Control.Exception (assert)
+import Control.Monad.ST (unsafeIOToST)
+import Data.Text.Internal (Text(..), empty)
+import qualified Data.Text.Array as A
+import Data.Word (Word16)
+import Foreign.Marshal.Alloc (allocaBytes)
+import Foreign.Ptr (Ptr, castPtr, plusPtr)
+import Foreign.Storable (peek, poke)
+
+-- $interop
+--
+-- The 'Text' type is implemented using arrays that are not guaranteed
+-- to have a fixed address in the Haskell heap. All communication with
+-- native code must thus occur by copying data back and forth.
+--
+-- The 'Text' type's internal representation is UTF-16, using the
+-- platform's native endianness. This makes copied data suitable for
+-- use with native libraries that use a similar representation, such
+-- as ICU. To interoperate with native libraries that use different
+-- internal representations, such as UTF-8 or UTF-32, consider using
+-- the functions in the 'Data.Text.Encoding' module.
+
+-- | /O(n)/ Create a new 'Text' from a 'Ptr' 'Word16' by copying the
+-- contents of the array.
+fromPtr :: Ptr Word16 -- ^ source array
+ -> Int -- ^ length of source array (in 'Word16' units)
+ -> IO Text
+fromPtr _ 0 = return empty
+fromPtr ptr len = assert (len > 0) $ return (Text arr 0 len)
+ where
+ arr = A.run (A.unsafeNew len >>= copy)
+ copy marr = loop ptr 0
+ where
+ loop !p !i | i == len = return marr
+ | otherwise = do
+ A.unsafeWrite marr i =<< unsafeIOToST (peek p)
+ loop (p `plusPtr` 2) (i + 1)
+
+-- | /O(1)/ Return the length of a 'Text' in units of 'Word16'. This
+-- is useful for sizing a target array appropriately before using
+-- 'unsafeCopyToPtr'.
+lengthWord16 :: Text -> Int
+lengthWord16 (Text _arr _off len) = len
+
+-- | /O(n)/ Copy a 'Text' to an array. The array is assumed to be big
+-- enough to hold the contents of the entire 'Text'.
+unsafeCopyToPtr :: Text -> Ptr Word16 -> IO ()
+unsafeCopyToPtr (Text arr off len) ptr = loop ptr off
+ where
+ end = off + len
+ loop !p !i | i == end = return ()
+ | otherwise = do
+ poke p (A.unsafeIndex arr i)
+ loop (p `plusPtr` 2) (i + 1)
+
+-- | /O(n)/ Perform an action on a temporary, mutable copy of a
+-- 'Text'. The copy is freed as soon as the action returns.
+useAsPtr :: Text -> (Ptr Word16 -> Int -> IO a) -> IO a
+useAsPtr t@(Text _arr _off len) action =
+ allocaBytes (len * 2) $ \buf -> do
+ unsafeCopyToPtr t buf
+ action (castPtr buf) len
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1  text.cabal
@@ -18,6 +18,7 @@ library
Data.Text
Data.Text.Encoding
Data.Text.Encoding.Fusion
+ Data.Text.Foreign
Data.Text.Fusion
other-modules:
Data.Text.Array
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