stream-element-type unset within pprint-logical-block

[Mark Cox]

The value of STREAM-ELEMENT-TYPE changes within a PPRINT-LOGICAL-BLOCK

(format t "~&Before: ~A~%" (stream-element-type *standard-output*))
(pprint-logical-block (*standard-output* nil)
  (format t "~&Logical Block: ~A~%" (stream-element-type *standard-output*)))

For the above code, SBCL 1.0.48.35 produces

Before: CHARACTER

Logical Block: NIL

[Matthias Benkard (mulk)]

The reason is that a PRETTY-STREAM is an ANSI-STREAM, so STREAM-ELEMENT-TYPE delegates to the ANSI-STREAM-MISC of the stream, which is SB-PRETTY::PRETTY-MISC for PRETTY-STREAMs. PRETTY-MISC returns NIL for (EQ OP :ELEMENT-TYPE). This is the definition:

(defun pretty-misc (stream op &optional arg1 arg2)
  (declare (ignore stream op arg1 arg2)))

I'm not sure what the fix should look like. Maybe something like this?

(defun pretty-misc (stream op &optional arg1 arg2)
  (declare (ignore arg1 arg2))
  (case op
    ((:element-type) (stream-element-type (pretty-stream-target stream)))))

Are there other -MISC features that PRETTY-STREAMs should hand through to the target stream?