Are port-column and port-line maintained by writes?

[Matthias Koeppe]

It seems to me that the current column and line of a port are not
updated by write operations; `port-column' and `port-line' always seem
to return 0.  This is not documented anywhere; if column and line are
not known, #f should be returned instead.

I would prefer having a useful implementation of these functions
available, though.  I suppose one would need to change `scm_lfwrite'
and/or `scm_c_write' to check for control characters; but I am not
sure about the differences between these two functions.  Can somebody
explain them to me?

(I was trying to fix the repl, so that the prompt always starts with a
fresh line, and to fix the ~& format directive to work with port
columns.  But I need `port-column' and `port-line' working for that.)

-- 
Matthias Köppe -- http://www.math.uni-magdeburg.de/~mkoeppe