Haskell help

So I got this arithmetic expression parser. I want to add subtraction and division support but I can't get it to work properly (aka make them left associative). Anyone got any ideas?:(

I import this:
http://www.cs.nott.ac.uk/~gmh/Parsing.lhs
then:
expr :: Parser Int
expr =  do t <- term
           do symbol "+"              
              e <- expr
              return (t+e)
            +++ return t

term :: Parser Int
term =  do f <- factor
           do symbol "*"
              t <- term
              return (f * t)
            +++ return f

factor :: Parser Int
factor =  do symbol "("
             e <- expr
             symbol ")"
             return e
           +++ natural

eval :: String -> Int
eval xs = case (parse expr xs) of
               [(n,[])]  -> n
               [(_,out)] -> error ("unused input " ++ out)
               []        -> error "invalid input"

>>2
>you're
IHBT