[project @ 2003-08-04 10:05:32 by ross]

[haskell-directory.git] / GHC / Read.lhs

diff --git a/GHC/Read.lhs b/GHC/Read.lhs
index 60805ff..bfffb19 100644 (file)
--- a/GHC/Read.lhs
+++ b/GHC/Read.lhs
@@ -50,7 +50,6 @@ import qualified Text.ParserCombinators.ReadP as P
 import Text.ParserCombinators.ReadP
   ( ReadP
   , readP_to_S
-  , readS_to_P
   )
 
 import qualified Text.Read.Lex as L
@@ -108,7 +107,9 @@ type ReadS a = String -> [(a,String)]
 class Read a where
   readsPrec    :: Int -> ReadS a
   readList     :: ReadS [a]
+  -- | Proposed replacement for 'readsPrec' using new-style parsers (GHC only).
   readPrec     :: ReadPrec a
+  -- | Proposed replacement for 'readList' using new-style parsers (GHC only).
   readListPrec :: ReadPrec [a]
   
   -- default definitions
@@ -118,13 +119,13 @@ class Read a where
   readListPrec = readS_to_Prec (\_ -> readList)
 
 readListDefault :: Read a => ReadS [a]
--- ^ Use this to define the 'readList' method, if you
---   don't want a special case
+-- ^ Use this to define the 'readList' method, if you don't want a special
+--   case (GHC only; for other systems the default suffices).
 readListDefault = readPrec_to_S readListPrec 0
 
 readListPrecDefault :: Read a => ReadPrec [a]
 -- ^ Use this to define the 'readListPrec' method, if you
---   don't want a special case
+--   don't want a special case (GHC only).
 readListPrecDefault = list readPrec
 
 ------------------------------------------------------------------------
@@ -158,13 +159,13 @@ lex :: ReadS String               -- As defined by H98
 lex s  = readP_to_S L.hsLex s
 
 lexLitChar :: ReadS String     -- As defined by H98
-lexLitChar = readP_to_S (do { P.skipSpaces ;
-                             (s, L.Char _) <- P.gather L.lex ;
+lexLitChar = readP_to_S (do { (s, _) <- P.gather L.lexChar ;
                              return s })
+       -- There was a skipSpaces before the P.gather L.lexChar,
+       -- but that seems inconsistent with readLitChar
 
 readLitChar :: ReadS Char      -- As defined by H98
-readLitChar = readP_to_S (do { L.Char c <- L.lex ;
-                              return c })
+readLitChar = readP_to_S L.lexChar
 
 lexDigits :: ReadS String
 lexDigits = readP_to_S (P.munch1 isDigit)
@@ -177,17 +178,17 @@ lexP :: ReadPrec L.Lexeme
 lexP = lift L.lex
 
 paren :: ReadPrec a -> ReadPrec a
--- ^ @(paren p)@ parses "(P0)"
---     where @p@ parses "P0" in precedence context zero
+-- ^ @(paren p)@ parses \"(P0)\"
+--     where @p@ parses \"P0\" in precedence context zero
 paren p = do L.Punc "(" <- lexP
             x          <- reset p
             L.Punc ")" <- lexP
             return x
 
 parens :: ReadPrec a -> ReadPrec a
--- ^ @(parens p)@ parses "P", "(P0)", "((P0))", etc, 
---     where @p@ parses "P"  in the current precedence context
---             parses "P0" in precedence context zero
+-- ^ @(parens p)@ parses \"P\", \"(P0)\", \"((P0))\", etc, 
+--     where @p@ parses \"P\"  in the current precedence context
+--             parses \"P0\" in precedence context zero
 parens p = optional
  where
   optional  = p +++ mandatory
@@ -217,7 +218,7 @@ list readx =
 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)]@
+--    @choose [(\"A\", return A), (\"B\", return B)]@
 choose sps = foldr ((+++) . try_one) pfail sps
           where
             try_one (s,p) = do { L.Ident s' <- lexP ;
@@ -290,10 +291,10 @@ to parse it in a context with a higher precedence level than k. But if
 there is one parenthesis parsed, then the required precedence level
 drops to 0 again, and parsing inside p may succeed.
 
-'appPrec' is just the precedence level of function application (maybe
-it should be called 'appPrec' instead).  So, if we are parsing
-function application, we'd better require the precedence level to be
-at least 'appPrec'. Otherwise, we have to put parentheses around it.
+'appPrec' is just the precedence level of function application.  So,
+if we are parsing function application, we'd better require the
+precedence level to be at least 'appPrec'. Otherwise, we have to put
+parentheses around it.
 
 'step' is used to increase the precedence levels inside a
 parser, and can be used to express left- or right- associativity. For