X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FRead.lhs;h=6305276cdd2bb352807d73cb966a883ecb446e82;hb=f827975d749073dbc8224fe74a3ee39393b26640;hp=d684a4a17592405f3eacd0e095700fe4711bdd3c;hpb=10de2c656f74562b662c22928be85e1b3ccda796;p=ghc-base.git

diff --git a/GHC/Read.lhs b/GHC/Read.lhs
index d684a4a..6305276 100644
--- a/GHC/Read.lhs
+++ b/GHC/Read.lhs
@@ -1,6 +1,7 @@
 \begin{code}
-{-# OPTIONS_GHC -XNoImplicitPrelude #-}
+{-# LANGUAGE CPP, NoImplicitPrelude, StandaloneDeriving #-}
 {-# OPTIONS_HADDOCK hide #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  GHC.Read
@@ -22,12 +23,6 @@ module GHC.Read
   -- ReadS type
   , ReadS      -- :: *; = String -> [(a,String)]
 
-  -- utility functions
-  , reads      -- :: Read a => ReadS a
-  , readp      -- :: Read a => ReadP a
-  , readEither -- :: Read a => String -> Either String a
-  , read       -- :: Read a => String -> a
-
   -- H98 compatibility
   , lex         -- :: ReadS String
   , lexLitChar  -- :: ReadS String
@@ -44,6 +39,9 @@ module GHC.Read
 
   -- Temporary
   , readParen
+
+  -- XXX Can this be removed?
+  , readp
   )
  where
 
@@ -64,17 +62,18 @@ import qualified Text.Read.Lex as L
 import Text.ParserCombinators.ReadPrec
 
 import Data.Maybe
-import Data.Either
 
 #ifndef __HADDOCK__
 import {-# SOURCE #-} GHC.Unicode       ( isDigit )
 #endif
 import GHC.Num
 import GHC.Real
-import GHC.Float
+import GHC.Float ()
 import GHC.Show
 import GHC.Base
 import GHC.Arr
+-- For defining instances for the generic deriving mechanism
+import GHC.Generics (Arity(..), Associativity(..), Fixity(..))
 \end{code}
 
 
@@ -225,33 +224,6 @@ readListPrecDefault :: Read a => ReadPrec [a]
 readListPrecDefault = list readPrec
 
 ------------------------------------------------------------------------
--- utility functions
-
--- | equivalent to 'readsPrec' with a precedence of 0.
-reads :: Read a => ReadS a
-reads = readsPrec minPrec
-
-readp :: Read a => ReadP a
-readp = readPrec_to_P readPrec 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)
-
-------------------------------------------------------------------------
 -- H98 compatibility
 
 -- | The 'lex' function reads a single lexeme from the input, discarding
@@ -345,10 +317,15 @@ choose :: [(String, ReadPrec a)] -> ReadPrec a
 -- ^ Parse the specified lexeme and continue as specified.
 -- Esp useful for nullary constructors; e.g.
 --    @choose [(\"A\", return A), (\"B\", return B)]@
+-- We match both Ident and Symbol because the constructor
+-- might be an operator eg (:=:)
 choose sps = foldr ((+++) . try_one) pfail sps
            where
-             try_one (s,p) = do { L.Ident s' <- lexP ;
-                                  if s == s' then p else pfail }
+             try_one (s,p) = do { token <- lexP ;
+                                  case token of
+                                    L.Ident s'  | s==s' -> p
+                                    L.Symbol s' | s==s' -> p
+                                    _other              -> pfail }
 \end{code}
 
 
@@ -448,23 +425,6 @@ instance Read a => Read (Maybe a) where
   readListPrec = readListPrecDefault
   readList     = readListDefault
 
-instance (Read a, Read b) => Read (Either a b) where
-  readPrec =
-    parens
-    ( prec appPrec
-      ( do L.Ident "Left" <- lexP
-           x            <- step readPrec
-           return (Left x)
-       +++
-        do L.Ident "Right" <- lexP
-           y             <- step readPrec
-           return (Right y)
-      )
-    )
-
-  readListPrec = readListPrecDefault
-  readList     = readListDefault
-
 instance Read a => Read [a] where
   readPrec     = readListPrec
   readListPrec = readListPrecDefault
@@ -473,9 +433,9 @@ instance Read a => Read [a] where
 instance  (Ix a, Read a, Read b) => Read (Array a b)  where
     readPrec = parens $ prec appPrec $
                do L.Ident "array" <- lexP
-                  bounds <- step readPrec
+                  theBounds <- step readPrec
                   vals   <- step readPrec
-                  return (array bounds vals)
+                  return (array theBounds vals)
 
     readListPrec = readListPrecDefault
     readList     = readListDefault
@@ -494,28 +454,28 @@ instance Read L.Lexeme where
 %*********************************************************
 
 \begin{code}
-readNumber :: Num a => (L.Lexeme -> Maybe a) -> ReadPrec a
+readNumber :: Num a => (L.Lexeme -> ReadPrec a) -> ReadPrec a
 -- Read a signed number
 readNumber convert =
   parens
   ( do x <- lexP
        case x of
-         L.Symbol "-" -> do n <- readNumber convert
+         L.Symbol "-" -> do y <- lexP
+                            n <- convert y
                             return (negate n)
-       
-         _   -> case convert x of
-                   Just n  -> return n
-                   Nothing -> pfail
+
+         _   -> convert x
   )
 
-convertInt :: Num a => L.Lexeme -> Maybe a
-convertInt (L.Int i) = Just (fromInteger i)
-convertInt _         = Nothing
 
-convertFrac :: Fractional a => L.Lexeme -> Maybe a
-convertFrac (L.Int i) = Just (fromInteger i)
-convertFrac (L.Rat r) = Just (fromRational r)
-convertFrac _         = Nothing
+convertInt :: Num a => L.Lexeme -> ReadPrec a
+convertInt (L.Int i) = return (fromInteger i)
+convertInt _         = pfail
+
+convertFrac :: Fractional a => L.Lexeme -> ReadPrec a
+convertFrac (L.Int i) = return (fromInteger i)
+convertFrac (L.Rat r) = return (fromRational r)
+convertFrac _         = pfail
 
 instance Read Int where
   readPrec     = readNumber convertInt
@@ -714,3 +674,18 @@ instance (Read a, Read b, Read c, Read d, Read e, Read f, Read g, Read h,
   readListPrec = readListPrecDefault
   readList     = readListDefault
 \end{code}
+
+\begin{code}
+-- XXX Can this be removed?
+
+readp :: Read a => ReadP a
+readp = readPrec_to_P readPrec minPrec
+\end{code}
+
+Instances for types of the generic deriving mechanism.
+
+\begin{code}
+deriving instance Read Arity
+deriving instance Read Associativity
+deriving instance Read Fixity
+\end{code}
\ No newline at end of file