common-lisp Streams Gray streams
Example
Gray streams are a non-standard extension that allows user defined streams. It provides classes and methods that the user can extend. You should check your implementations manual to see if it provides Gray streams.
For a simple example, a character input stream that returns random characters could be implemented like this:
(defclass random-character-input-stream (fundamental-character-input-stream)
((character-table
:initarg :character-table
:initform "abcdefghijklmnopqrstuvwxyz
" ; The newline is necessary.
:accessor character-table))
(:documentation "A stream of random characters."))
(defmethod stream-read-char ((stream random-character-input-stream))
(let ((table (character-table stream)))
(aref table (random (length table)))))
(let ((stream (make-instance 'random-character-input-stream)))
(dotimes (i 5)
(print (read-line stream))))
; "gyaexyfjsqdcpciaaftoytsygdeycrrzwivwcfb"
; "gctnoxpajovjqjbkiqykdflbhfspmexjaaggonhydhayvknwpdydyiabithpt"
; "nvfxwzczfalosaqw"
; "sxeiejcovrtesbpmoppfvvjfvx"
; "hjplqgstbodbalnmxhsvxdox"
;=> NIL
