<div class="gmail_quote">On Fri, Jun 19, 2009 at 11:18 AM, Paulo J. Matos <<a href="mailto:pocmatos@gmail.com">pocmatos@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> Still on this, is it not possible to re-insert a char in an input-port? This way, once the lexer recognizes a one-line comment I could re-insert the \n into the port and keep lexing... <div></div></blockquote><div> If you are reading from either a file or string port, then you can use file-position to rewind the port to the correct position so the next lex will start from the correct place. <a href="http://docs.plt-scheme.org/reference/port-buffers.html#(def._((quote._~23~25kernel)._file-position))">http://docs.plt-scheme.org/reference/port-buffers.html#(def._((quote._~23~25kernel)._file-position))</a> Another approach is to use lexer to only handle the start of the comment, e.g., // and then write your own custom reader to read until it hits newline (but preserving it), and then hand the control back to the lexer. (define (custom-comment-reader in) (read-until-new-line ...)) ;; defined elsewhere (define eb-lexer (lexer ("//" (custom-comment-reader input-port) ...) ...)) Cheers, yc </div></div>