[Haskell] Parsec operator issue

[Adam Crume]

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"                                       
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