[Haskell-cafe] Error detection in GLR Happy grammar

Hi! I'm trying to detect parse errors in a happy GLR grammar, but I can't! I insert the special "token" 'error', and call the error function when an error is found. However, the program prints no error messages, and simply returns a ParseError at the end. Does any of you have an good example of a GLR parser with error detection and, if possible, error recovery as well?