X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Text%2FRead.hs;h=5ab8877efc080a44a955175fb1f678e5f79a149d;hb=0001f92b790079cec9df03c2229d6f39268f60af;hp=16a4d158eeb701b09d543019d768c866bbc4d0e5;hpb=aaf764b3ad8b1816d68b5f27299eac125f08e1a5;p=ghc-base.git

diff --git a/Text/Read.hs b/Text/Read.hs
index 16a4d15..5ab8877 100644
--- a/Text/Read.hs
+++ b/Text/Read.hs
@@ -1,4 +1,4 @@
-{-# OPTIONS_GHC -fno-implicit-prelude #-}
+{-# OPTIONS_GHC -XNoImplicitPrelude #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Text.Read
@@ -21,39 +21,80 @@
 
 module Text.Read (
    -- * The 'Read' class
-   Read(..),		-- The Read class
-   ReadS, 		-- String -> Maybe (a,String)
+   Read(..),            -- The Read class
+   ReadS,               -- String -> Maybe (a,String)
 
    -- * Haskell 98 functions
-   reads,		-- :: (Read a) => ReadS a
-   read,		-- :: (Read a) => String -> a
-   readParen, 		-- :: Bool -> ReadS a -> ReadS a
-   lex,			-- :: ReadS String
+   reads,               -- :: (Read a) => ReadS a
+   read,                -- :: (Read a) => String -> a
+   readParen,           -- :: Bool -> ReadS a -> ReadS a
+   lex,                 -- :: ReadS String
 
 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
    -- * New parsing functions
    module Text.ParserCombinators.ReadPrec,
-   L.Lexeme(..),	
-   lexP,		-- :: ReadPrec Lexeme
+   L.Lexeme(..),
+   lexP,                -- :: ReadPrec Lexeme
+   parens,              -- :: ReadPrec a -> ReadPrec a
 #endif
 #ifdef __GLASGOW_HASKELL__
-   readListDefault,	-- :: Read a => ReadS [a]
-   readListPrecDefault,	-- :: Read a => ReadPrec [a]
+   readListDefault,     -- :: Read a => ReadS [a]
+   readListPrecDefault, -- :: Read a => ReadPrec [a]
 #endif
 
  ) where
 
 #ifdef __GLASGOW_HASKELL__
+import GHC.Base
 import GHC.Read
-#endif   
+import Data.Either
+import Text.ParserCombinators.ReadP as P
+#endif
 #if defined(__GLASGOW_HASKELL__) || defined(__HUGS__)
 import Text.ParserCombinators.ReadPrec
 import qualified Text.Read.Lex as L
-#endif   
+#endif
 
 #ifdef __HUGS__
 -- copied from GHC.Read
 
 lexP :: ReadPrec L.Lexeme
 lexP = lift L.lex
+
+parens :: ReadPrec a -> ReadPrec a
+parens p = optional
+ where
+  optional  = p +++ mandatory
+  mandatory = do
+    L.Punc "(" <- lexP
+    x          <- reset optional
+    L.Punc ")" <- lexP
+    return x
+#endif
+
+#ifdef __GLASGOW_HASKELL__
+------------------------------------------------------------------------
+-- utility functions
+
+-- | equivalent to 'readsPrec' with a precedence of 0.
+reads :: Read a => ReadS a
+reads = readsPrec minPrec
+
+readEither :: Read a => String -> Either String a
+readEither s =
+  case [ x | (x,"") <- readPrec_to_S read' minPrec s ] of
+    [x] -> Right x
+    []  -> Left "Prelude.read: no parse"
+    _   -> Left "Prelude.read: ambiguous parse"
+ where
+  read' =
+    do x <- readPrec
+       lift P.skipSpaces
+       return x
+
+-- | The 'read' function reads input from a string, which must be
+-- completely consumed by the input process.
+read :: Read a => String -> a
+read s = either error id (readEither s)
 #endif
+