\verb;read-st; converts Scheme\TeX{} representations of Scheme objects
into the objects themselves much as \verb;read; does. It uses the
non-standard, but generally available routine \verb;peek-char;.
(define (read-st . rest) ; Returns what \verb;read; returns.
(let ((port (if (pair? rest) ; \verb;read-st; arguments are
(car rest) ; the same as \verb;read;'s.
(current-input-port))))
(letrec ; Lines of a Scheme\TeX{} file
(((text-mode-and-saw-newline) ; beginning with ``{\tt(}'',
(let ((ch (peek-char port))) ; start a code section.
(cond ((eof-object? ch) ch)
((char=? ch #\() ; If code section, then use
(got-code (read port))) ; \verb;read; to get code,
(else ; else skip this line as
(text-mode-within-a-line))))) ; it is a comment.
((text-mode-within-a-line)
(let ((ch (read-char port)))
(cond ((eof-object? ch) ch)
((char=? ch #\newline)
(text-mode-and-saw-newline))
(else (text-mode-within-a-line)))))
((got-code code) ; Ignore the remainder of the
(let ((ch (read-char port))) ; last code line and return
(cond ((eof-object? ch) code) ; the results of \verb;read;.
((char=? ch #\newline)
code)
(else (got-code code))))))
(text-mode-and-saw-newline) ; Start by looking
))) ; for a code line.
\end{document}
