make-synonym-stream

(make-synonym-stream symbol)

Returns a stream that forwards every operation to the stream the special variable symbol holds at the time of that operation -- so rebinding the variable afterwards redirects a synonym stream that was constructed earlier. The usual shape is a defvar whose default output follows whatever the standard stream currently is.

The result is a stream value, not a designator: it is true, streamp / input-stream-p / output-stream-p answer t for it, synonym-stream-symbol reads the symbol back, and close closes the synonym (which is nothing to do) and answers t.

A Gray stream may sit on either side of it: a synonym stream handed to a Gray output stream is written through, and a synonym whose variable holds a Gray stream reaches it.