Hi Adam,

parse "x=-1", it fails. Does anyone know how to fix this?

This issue is in using the 'reservedOp' combinator which rejects '=' when followed by '-'.    reservedOp name =        lexeme $ try $        do{ string name          ; notFollowedBy (opLetter languageDef) <?> ("end of " ++ show name)          } If you change: reservedOp "=" to: char '=' then your test passes. -Greg On Tue, Feb 16, 2010 at 2:10 PM, Adam Crume <adamcrume@hotmail.com> wrote:

I have a parser with a prefix "-" and an infix "=".  When I try to parse "x=-1", it fails.  Does anyone know how to fix this? I stripped my code down as much as possible.  It parses "x=1" and "-1", but fails for "x=-1".

import Text.Parsec import qualified Text.Parsec.Expr as PE import qualified Text.Parsec.Language as L import qualified Text.Parsec.Token as T

lexer = T.makeTokenParser L.emptyDef {T.reservedOpNames = ["=", "-"]}

reservedOp = T.reservedOp lexer

integer = T.integer lexer >> return ""

symbol = T.identifier lexer

expression = PE.buildExpressionParser table (integer <|> symbol)     where          table = [ [ PE.Prefix (reservedOp "-" >> return (\x-> "")) ],                    [ PE.Infix (reservedOp "=" >> return (\x-> \y->"")) PE.AssocRight ] ]

input = do   e <- expression   eof   return e

testParse s = case (parse input "(unknown)" s) of                   Left f -> putStrLn $ s ++ "\n" ++ show f                   Right f -> putStrLn s

main = do   testParse "x=1"   testParse "-1"   testParse "x=-1" ________________________________ Hotmail: Free, trusted and rich email service. Get it now. _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell