alex posn

lex.x

scan :: String -> Pipeline [Token]
scan str = go (alexStartPos, '\n', [], str)
    where
        go inp@(pos, _, _, str) = case alexScan inp 0 of
            AlexEOF -> return []
            AlexError (pos, _, _, _) -> throwError $ LexError (toPosition pos) "fucked up"
            AlexSkip  inp_ len     -> go inp_
            AlexToken inp_ len act -> do
                xs <- go inp_
                return $ act pos (take len str) : xs