[Haskell-cafe] buildExpressionParser prefix recursion

I was wondering why Parsec's buildExpressionParser doesn't allow prefix expressions to be handled recursively, e.g. given a prefix "!" operation, it seems that "!!a" could parse without requiring parentheses ("!(!a)"). Is there an easy way to extend it? (I have a rich expression grammar I'd like to parse which includes several prefix forms, and it would be a shame to have to abandon buildExpressionParser since it is so concise and convenient.) Thanks, Warren