X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Text%2FRead.hs;h=d935ffec419dfff7dda5c8b8d7b4f9e71ef0e218;hb=7a97ec4b12e1fbec5505f82032cf4dc435b5a60c;hp=bf70920138eeaa22d8e5e0434d8560eb1c86a8c7;hpb=2ed749d45e044d5793a8d150c3ee226aca206773;p=ghc-base.git

diff --git a/Text/Read.hs b/Text/Read.hs
index bf70920..d935ffe 100644
--- a/Text/Read.hs
+++ b/Text/Read.hs
@@ -1,4 +1,5 @@
-{-# OPTIONS -fno-implicit-prelude #-}
+{-# LANGUAGE CPP, NoImplicitPrelude #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Text.Read
@@ -7,38 +8,94 @@
 -- 
 -- Maintainer  :  libraries@haskell.org
 -- Stability   :  provisional
--- Portability :  portable
+-- Portability :  non-portable (uses Text.ParserCombinators.ReadP)
+--
+-- Converting strings to values.
 --
 -- The "Text.Read" library is the canonical library to import for
--- 'Read'-class facilities.  It offers an extended and much improved
--- 'Read' class, which constitutes a proposed alternative to the 
--- Haskell98 'Read'.  In particular, writing parsers is easier, and
+-- 'Read'-class facilities.  For GHC only, it offers an extended and much
+-- improved 'Read' class, which constitutes a proposed alternative to the 
+-- Haskell 98 'Read'.  In particular, writing parsers is easier, and
 -- the parsers are much more efficient.
 --
 -----------------------------------------------------------------------------
 
 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
-   readListDefault,	-- :: Read a => ReadS [a]
-   readListPrecDefault,	-- :: Read a => ReadPrec [a]
+   L.Lexeme(..),
+   lexP,                -- :: ReadPrec Lexeme
+   parens,              -- :: ReadPrec a -> ReadPrec a
+#endif
+#ifdef __GLASGOW_HASKELL__
+   readListDefault,     -- :: Read a => ReadS [a]
+   readListPrecDefault, -- :: Read a => ReadPrec [a]
+#endif
 
  ) where
 
 #ifdef __GLASGOW_HASKELL__
+import GHC.Base
 import GHC.Read
+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
+