Data/Text/Show.hs

    {-# LANGUAGE CPP, MagicHash #-}
    {-# OPTIONS_GHC -fno-warn-orphans #-}
    #if __GLASGOW_HASKELL__ >= 702
    {-# LANGUAGE Trustworthy #-}
    #endif

    -- |
    -- Module      : Data.Text.Show
    -- Copyright   : (c) 2009-2015 Bryan O'Sullivan
    --
    -- License     : BSD-style
    -- Maintainer  : bos@serpentine.com
    -- Stability   : experimental
    -- Portability : GHC

    module Data.Text.Show
        (
          singleton
        , unpack
        , unpackCString#
        ) where

    import Control.Monad.ST (ST)
    import Data.Text.Internal (Text(..), empty_, safe)
    import Data.Text.Internal.Fusion (stream, unstream)
    import Data.Text.Internal.Unsafe.Char (unsafeWrite)
    import GHC.Prim (Addr#)
    import qualified Data.Text.Array as A
    import qualified Data.Text.Internal.Fusion.Common as S

    #if __GLASGOW_HASKELL__ >= 702
    import qualified GHC.CString as GHC
    #else
    import qualified GHC.Base as GHC
    #endif

    instance Show Text where
        showsPrec p ps r = showsPrec p (unpack ps) r

    -- | /O(n)/ Convert a 'Text' into a 'String'.  Subject to fusion.
    unpack :: Text -> String
    unpack = S.unstreamList . stream
    {-# INLINE [1] unpack #-}

    -- | /O(n)/ Convert a literal string into a 'Text'.  Subject to
    -- fusion.
    --
    -- This is exposed solely for people writing GHC rewrite rules.
    --
    -- @since 1.2.1.1
    unpackCString# :: Addr# -> Text
    unpackCString# addr# = unstream (S.streamCString# addr#)
    {-# NOINLINE unpackCString# #-}

    {-# RULES "TEXT literal" [1] forall a.
        unstream (S.map safe (S.streamList (GHC.unpackCString# a)))
          = unpackCString# a #-}

    {-# RULES "TEXT literal UTF8" [1] forall a.
        unstream (S.map safe (S.streamList (GHC.unpackCStringUtf8# a)))
          = unpackCString# a #-}

    {-# RULES "TEXT empty literal" [1]
        unstream (S.map safe (S.streamList []))
          = empty_ #-}

    {-# RULES "TEXT singleton literal" [1] forall a.
        unstream (S.map safe (S.streamList [a]))
          = singleton_ a #-}

    -- | /O(1)/ Convert a character into a Text.  Subject to fusion.
    -- Performs replacement on invalid scalar values.
    singleton :: Char -> Text
    singleton = unstream . S.singleton . safe
    {-# INLINE [1] singleton #-}

    {-# RULES "TEXT singleton" forall a.
        unstream (S.singleton (safe a))
          = singleton_ a #-}

    -- This is intended to reduce inlining bloat.
    singleton_ :: Char -> Text
    singleton_ c = Text (A.run x) 0 len
      where x :: ST s (A.MArray s)
            x = do arr <- A.new len
                   _ <- unsafeWrite arr 0 d
                   return arr
            len | d < '\x10000' = 1
                | otherwise     = 2
            d = safe c
    {-# NOINLINE singleton_ #-}