Add Data.Text.Lazy.Read

--HG--
extra : convert_revision : 576014657158d70ea6a333a21be2fe61d014cf2a

Data/Text/Lazy/Read.hs

@@ -0,0 +1,155 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+-- |
+-- Module      : Data.Text.Lazy.Read
+-- Copyright   : (c) 2010 Bryan O'Sullivan
+--
+-- License     : BSD-style
+-- Maintainer  : bos@serpentine.com, rtomharper@googlemail.com,
+--               duncan@haskell.org
+-- Stability   : experimental
+-- Portability : GHC
+--
+-- Functions used frequently when reading textual data.
+module Data.Text.Lazy.Read
+    (
+      Reader
+    , decimal
+    , hexadecimal
+    , signed
+    , rational
+    , double
+    ) where
+
+import Control.Monad (liftM)
+import Data.Char (digitToInt, isDigit, isHexDigit, ord)
+import Data.Ratio
+import Data.Text.Lazy as T
+
+-- | Read some text, and if the read succeeds, return its value and
+-- the remaining text.
+type Reader a = Text -> Either String (a,Text)
+
+-- | Read a decimal integer.
+--
+-- This function does not handle leading sign characters.  If you need
+-- to handle signed input, use @'signed' 'decimal'@.
+decimal :: Integral a => Reader a
+{-# SPECIALIZE decimal :: Reader Int #-}
+{-# SPECIALIZE decimal :: Reader Integer #-}
+decimal txt
+    | T.null h  = Left "no digits in input"
+    | otherwise = Right (T.foldl' go 0 h, t)
+  where (h,t)  = T.spanBy isDigit txt
+        go n d = (n * 10 + fromIntegral (digitToInt d))
+
+-- | Read a hexadecimal number, with optional leading @\"0x\"@.  This
+-- function is case insensitive.
+--
+-- This function does not handle leading sign characters.  If you need
+-- to handle signed input, use @'signed' 'hexadecimal'@.
+hexadecimal :: Integral a => Reader a
+{-# SPECIALIZE hex :: Reader Int #-}
+{-# SPECIALIZE hex :: Reader Integer #-}
+hexadecimal txt
+    | T.toLower h == "0x" = hex t
+    | otherwise           = hex txt
+ where (h,t) = T.splitAt 2 txt
+
+-- | Read a leading sign character (@\'-\'@ or @\'+\'@) and apply it
+-- to the result of applying the given reader.
+signed :: Num a => Reader a -> Reader a
+{-# INLINE signed #-}
+signed f = runP (signa (P f))
+
+-- | Read a rational number.
+--
+-- This function accepts an optional leading sign character.
+rational :: RealFloat a => Reader a
+{-# SPECIALIZE rational :: Reader Double #-}
+rational = floaty $ \real frac fracDenom -> fromRational $
+                     real % 1 + frac % fracDenom
+
+-- | Read a rational number.
+--
+-- This function accepts an optional leading sign character.
+--
+-- /Note/: This function is almost ten times faster than 'rational',
+-- but is slightly less accurate.
+--
+-- The 'Double' type supports about 16 decimal places of accuracy.
+-- For 94.2% of numbers, this function and 'rational' give identical
+-- results, but for the remaining 5.8%, this function loses precision
+-- around the 15th decimal place.  For 0.001% of numbers, this
+-- function will lose precision at the 13th or 14th decimal place.
+double :: Reader Double
+double = floaty $ \real frac fracDenom ->
+                   fromIntegral real +
+                   fromIntegral frac / fromIntegral fracDenom
+
+hex :: Integral a => Reader a
+{-# SPECIALIZE hex :: Reader Int #-}
+{-# SPECIALIZE hex :: Reader Integer #-}
+hex txt
+    | T.null h  = Left "no digits in input"
+    | otherwise = Right (T.foldl' go 0 h, t)
+  where (h,t)  = T.spanBy isHexDigit txt
+        go n d = (n * 16 + fromIntegral (hexDigitToInt d))
+
+hexDigitToInt :: Char -> Int
+hexDigitToInt c
+    | c >= '0' && c <= '9' = ord c - ord '0'
+    | c >= 'a' && c <= 'f' = ord c - (ord 'a' - 10)
+    | c >= 'A' && c <= 'F' = ord c - (ord 'A' - 10)
+    | otherwise            = error "Data.Text.Lex.hexDigitToInt: bad input"
+
+signa :: Num a => Parser a -> Parser a
+{-# SPECIALIZE signa :: Parser Int -> Parser Int #-}
+{-# SPECIALIZE signa :: Parser Integer -> Parser Integer #-}
+signa p = do
+  sign <- perhaps '+' $ char (\c -> c == '-' || c == '+')
+  if sign == '+' then p else negate `liftM` p
+
+newtype Parser a = P {
+      runP :: Text -> Either String (a,Text)
+    }
+
+instance Monad Parser where
+    return a = P $ \t -> Right (a,t)
+    {-# INLINE return #-}
+    m >>= k  = P $ \t -> case runP m t of
+                           Left err     -> Left err
+                           Right (a,t') -> runP (k a) t'
+    {-# INLINE (>>=) #-}
+    fail msg = P $ \_ -> Left msg
+
+perhaps :: a -> Parser a -> Parser a
+perhaps def m = P $ \t -> case runP m t of
+                            Left _      -> Right (def,t)
+                            r@(Right _) -> r
+
+char :: (Char -> Bool) -> Parser Char
+char p = P $ \t -> case T.uncons t of
+                     Just (c,t') | p c -> Right (c,t')
+                     _                 -> Left "char"
+
+data T = T !Integer !Int
+
+floaty :: RealFloat a => (Integer -> Integer -> Integer -> a) -> Reader a
+{-# INLINE floaty #-}
+floaty f = runP $ do
+  real <- signa (P decimal)
+  T fraction fracDigits <- perhaps (T 0 0) $ do
+    _ <- char (=='.')
+    digits <- P $ \t -> Right (fromIntegral . T.length $ T.takeWhile isDigit t, t)
+    n <- P decimal
+    return $ T n digits
+  let e c = c == 'e' || c == 'E'
+  power <- perhaps 0 (char e >> signa (P decimal) :: Parser Int)
+  return $! if fracDigits == 0
+            then if power == 0
+                 then fromIntegral real
+                 else fromIntegral real * (10 ^^ power)
+            else if power == 0
+                 then f real fraction (10 ^ fracDigits)
+                 else f real fraction (10 ^ fracDigits) * (10 ^^ power)

Data/Text/Read.hs

@@ -10,7 +10,7 @@
 -- Stability   : experimental
 -- Portability : GHC
 --
--- Reading functions used frequently when handling textual data.
+-- Functions used frequently when reading textual data.
 module Data.Text.Read
     (
       Reader

text.cabal

@@ -78,6 +78,7 @@ library
     Data.Text.Lazy.Builder
     Data.Text.Lazy.Encoding
     Data.Text.Lazy.IO
+    Data.Text.Lazy.Read
     Data.Text.Read
   other-modules:
     Data.Text.Array