




The generic function stream-line-column returns the column number where the next character will be written from stream, or nil if this is not meaningful for the stream. This function is used in the implementation of print and the format ~t directive. A method for this function must be defined for every character output stream class that is defined, although at its simplest it may be defined to always return nil.
LispWorks User Guide and Reference Manual - 20 Sep 2017