make-broadcast-stream

(make-broadcast-stream &rest streams)

An output stream that fans every write out to each component stream, in the order given. With no components it is the discarding sink instead: writes to it are dropped (the CL idiom for a null output stream).

A broadcast stream WITH components is a Gray stream, so it takes the whole output protocol: format, princ, prin1, print, write-string, write-char, terpri, fresh-line, write-line, force-output, finish-output, clear-output and close. fresh-line always writes a newline on one: a broadcast stream tracks no column, so it cannot tell whether it is already at the start of a line.