The class fundamental-character-output-stream
provides default methods for generic functions used for character output, and should therefore be included by stream classes concerned with character output. The user can provide methods for these generic functions specialized on the user-defined class. Methods for other generic functions must be provided by the user.
There is an example in Defining a new stream class.
fundamental-character-stream
fundamental-input-stream
stream-clear-output
stream-finish-output
stream-force-output
stream-start-line-p
stream-terpri
stream-line-column
stream-write-char
stream-write-sequence
stream-write-string
LispWorks User Guide and Reference Manual - 20 Sep 2017