diff options
| -rw-r--r-- | libraries/base/GHC/Read.lhs | 29 | ||||
| -rw-r--r-- | libraries/base/Text/Read/Lex.hs | 7 |
2 files changed, 22 insertions, 14 deletions
diff --git a/libraries/base/GHC/Read.lhs b/libraries/base/GHC/Read.lhs index c5024fc1a6..c54227477f 100644 --- a/libraries/base/GHC/Read.lhs +++ b/libraries/base/GHC/Read.lhs @@ -32,7 +32,7 @@ module GHC.Read , lexDigits -- defining readers - , lexP + , lexP, expectP , paren , parens , list @@ -270,12 +270,15 @@ lexP :: ReadPrec L.Lexeme -- ^ Parse a single lexeme lexP = lift L.lex +expectP :: L.Lexeme -> ReadPrec () +expectP lexeme = lift (L.expect lexeme) + paren :: ReadPrec a -> ReadPrec a -- ^ @(paren p)@ parses \"(P0)\" -- where @p@ parses \"P0\" in precedence context zero -paren p = do L.Punc "(" <- lexP - x <- reset p - L.Punc ")" <- lexP +paren p = do expectP (L.Punc "(") + x <- reset p + expectP (L.Punc ")") return x parens :: ReadPrec a -> ReadPrec a @@ -292,7 +295,7 @@ list :: ReadPrec a -> ReadPrec [a] -- using the usual square-bracket syntax. list readx = parens - ( do L.Punc "[" <- lexP + ( do expectP (L.Punc "[") (listRest False +++ listNext) ) where @@ -408,12 +411,12 @@ parenthesis-like objects such as (...) and [...] can be an argument to instance Read a => Read (Maybe a) where readPrec = parens - (do L.Ident "Nothing" <- lexP + (do expectP (L.Ident "Nothing") return Nothing +++ prec appPrec ( - do L.Ident "Just" <- lexP - x <- step readPrec + do expectP (L.Ident "Just") + x <- step readPrec return (Just x)) ) @@ -427,7 +430,7 @@ 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 + do expectP (L.Ident "array") theBounds <- step readPrec vals <- step readPrec return (array theBounds vals) @@ -504,9 +507,9 @@ instance (Integral a, Read a) => Read (Ratio a) where readPrec = parens ( prec ratioPrec - ( do x <- step readPrec - L.Symbol "%" <- lexP - y <- step readPrec + ( do x <- step readPrec + expectP (L.Symbol "%") + y <- step readPrec return (x % y) ) ) @@ -543,7 +546,7 @@ wrap_tup :: ReadPrec a -> ReadPrec a wrap_tup p = parens (paren p) read_comma :: ReadPrec () -read_comma = do { L.Punc "," <- lexP; return () } +read_comma = expectP (L.Punc ",") read_tup2 :: (Read a, Read b) => ReadPrec (a,b) -- Reads "a , b" no parens! diff --git a/libraries/base/Text/Read/Lex.hs b/libraries/base/Text/Read/Lex.hs index f5a07f1658..8a64e21b80 100644 --- a/libraries/base/Text/Read/Lex.hs +++ b/libraries/base/Text/Read/Lex.hs @@ -22,7 +22,7 @@ module Text.Read.Lex , numberToInteger, numberToRational, numberToRangedRational -- lexer - , lex + , lex, expect , hsLex , lexChar @@ -144,6 +144,11 @@ numberToRational (MkDecimal iPart mFPart mExp) lex :: ReadP Lexeme lex = skipSpaces >> lexToken +expect :: Lexeme -> ReadP () +expect lexeme = do { skipSpaces + ; thing <- lexToken + ; if thing == lexeme then return () else pfail } + hsLex :: ReadP String -- ^ Haskell lexer: returns the lexed string, rather than the lexeme hsLex = do skipSpaces |