Commit 76f008da authored by Richard M. Stallman's avatar Richard M. Stallman
Browse files

(Using Interactive): Explain problem of markers, etc., in command-history.

parent ac2c5120
......@@ -233,6 +233,20 @@ reading the keyboard input:
(let ((string (read-string "Foo: " nil 'my-history)))
(list (region-beginning) (region-end) string)))
@end smallexample
@strong{Warning:} the argument values should not include any data
types that can't be printed and then read. Some facilities save
@code{command-history} in a file to be read in the subsequent
sessions; if a command's arguments contain a data type that prints
using @samp{#<@dots{}>} syntax, those facilities won't work.
There are, however, a few exceptions: it is ok to use a limited set of
expressions such as @code{(point)}, @code{(mark)},
@code{(region-beginning)}, and @code{(region-end)}, because Emacs
recognizes them specially and puts the expression (rather than its
value) into the command history. To see whether the expression you
wrote is one of these exceptions, run the command, then examine
@code{(car command-history)}.
@end itemize
@cindex examining the @code{interactive} form
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