From: "Drew Adams" <drew.adams@oracle.com>
Subject: RE: message in minibuffer
Date: Sat, 19 Nov 2005 22:58:52 -0800 [thread overview]
Message-ID: <DNEMKBNJBGPAOPIJOOICKEBCCPAA.drew.adams@oracle.com> (raw)
In-Reply-To: <1132465960.466513.6320@g49g2000cwa.googlegroups.com>
Here is a sample piece of code
(defun foo () (let ((arg "abc")) (message "Here is arg: %s" arg)))
I evaluate this in the minibuffer
Eval: (foo)
and get "Here is arg: abc"
in the [echo area]. However if I evaluate it with
M-x foo
I get the output Here is arg: abc
It seems that the quotation marks show up depending on how the function
is invoked. Why?
Like many "functions" in Lisp, `message' does two things:
1. It displays a message in the minibuffer.
2. It returns a value: the message that it displayed - a string.
#1 is a side effect. #2 is the normal behavior of a true function.
But this is more than a question just of `message'...
When you evaluate `(foo)' using, for example, `M-:' (command
`eval-expression'), you see only the result of the evaluation - that's the
behavior of `eval-expression' (it's own side effect): print the result of
evaluation in the echo area. When the string value of `message' is printed,
it is enclosed in double-quotes, so you can see that the value is a string.
In fact, the process of evaluating `M-: (foo)' first calls (message...),
which prints your message (without quotes), but then the result of `M-:
(foo)' is printed (as a string - showing the quotes), so you never see the
first message. If you check buffer *Messages*, you will see your message,
without the quotes.
When you evaluate `(message...)' using `M-x foo', the result of the
evaluation (of `(foo)') is not echoed in the echo area, because function
`execute-extended-command' (which is bound to `M-x') does not have such a
side effect.
IOW, this is all about 1) keeping straight the difference between side
effect and resulting value, and 2) knowing the behavior of the given
functions (`eval-expression' vs `execute-extended-command').
"Are we having fun yet?", asks Zippy, tossing his "Elementary Haskell"
manual into the dryer and turning the dial to "Delicates". "We'll see if
it's really Purely Functional and 100% Fully Lazy..."
HTH.
next prev parent reply other threads:[~2005-11-20 6:58 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-11-19 23:52 message in minibuffer wkomornicki
2005-11-20 0:10 ` Drew Adams
[not found] ` <mailman.15965.1132445463.20277.help-gnu-emacs@gnu.org>
2005-11-20 5:52 ` wkomornicki
2005-11-20 6:58 ` Drew Adams [this message]
[not found] ` <mailman.15984.1132469952.20277.help-gnu-emacs@gnu.org>
2005-11-20 20:15 ` wkomornicki
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=DNEMKBNJBGPAOPIJOOICKEBCCPAA.drew.adams@oracle.com \
--to=drew.adams@oracle.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this external index
https://git.savannah.gnu.org/cgit/emacs.git
https://git.savannah.gnu.org/cgit/emacs/org-mode.git
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.