It looks like it's done here in the print routine: https://github.com/JeffBezanson/femtolisp/blob/master/print.c#L423 https://github.com/JeffBezanson/femtolisp/

It looks like it's done here in the print routine: https://github.com/JeffBezanson/femtolisp/blob/master/print.c#L423 https://github.com/JeffBezanson/femtolisp/blob/master/print.... It adds 48 to each byte being printed, which is ASCII '0'.