Re: [Haskell-cafe] problem with happy

The lexer was wrong - but it was the lexer function not the lexer spec - try the one below. Note that you have to take 'len' chars from the original input. Previously you were taking the whole of the "rest-of--input": lexer :: (TheToken -> P a) -> P a lexer f input@(_,_,instr) = case alexScan input 0 of AlexEOF -> f Eof input AlexError (pos, _, _) -> Failed $ showPos pos ++ ": lexical error" AlexSkip input' len -> lexer f input' AlexToken (pos, c, str) len act -> let (Token newpos thetok) = act pos (take len instr) in f thetok (newpos, c, str)