These procedures are in structure extended-ports.
(make-string-input-port string) -> input-port
(make-string-output-port) -> output-port
(string-output-port-output string-output-port) -> string
Make-string-input-port returns an input port that
that reads characters from the supplied string. An end-of-file
object is returned if the user reads past the end of the string.
Make-string-output-port returns an output port that saves
the characters written to it.
These are then returned as a string by string-output-port-output.
(read (make-string-input-port "(a b)"))
-> '(a b)
(let ((p (make-string-output-port)))
(write '(a b) p)
(let ((s (string-output-port-output p)))
(display "c" p)
(list s (string-output-port-output p))))
-> '("(a b)" "(a b)c")
limit-output returns.
If procedure returns before writing n characters, then
limit-output also returns at that time, regardless of how many
characters have been written.
(make-tracking-input-port input-port) -> input-port
(make-tracking-output-port output-port) -> output-port
(current-row port) -> integer or #f
(current-column port) -> integer or #f
(fresh-line output-port)
Make-tracking-input-port and make-tracking-output-port
return ports that keep track of the current row and column and
are otherwise identical to their arguments.
Closing a tracking port does not close the underlying port.
Current-row and current-column return
port's current read or write location.
They return #f if port does not keep track of its location.
Fresh-line writes a newline character to output-port if
(current-row port) is not 0.
(define p (open-output-port "/tmp/temp"))
(list (current-row p) (current-column p))
-> '(0 0)
(display "012" p)
(list (current-row p) (current-column p))
-> '(0 3)
(fresh-line p)
(list (current-row p) (current-column p))
-> '(1 0)
(fresh-line p)
(list (current-row p) (current-column p))
-> '(1 0)
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