read-one-special in readable-snip<%>
( -> three values: an arbitrary value, an exact non-negative integer, and a boolean
send a-readable-snip read-one-special index source line column position)
index : exact non-negative integer
source : value
line : exact non-negative integer or #f
column : exact non-negative integer or #f
position : exact non-negative integer or #f
The index argument is 0 the first time this method is
called for a particular output stream. If the last result value is
#f, then the method is called again to obtain additional
results, and index is incremented for each call.
The remaining arguments are the same as the arguments to a procedure
returned by a custom input port's read-string-proc; see
Custom Ports, section 11.1.6 in PLT MzScheme: Language Manual for details. The first two
results are also the same as the results from a
read-string-proc-produced procedure.
If the method raises exn:special-comment, the exception is
used in the same way as when a custom import port raises the
exception. The method will not be called for additional results
in that case.