message in minibuffer

message in minibuffer

[wkomornicki]

I am a newbie in writing lisp code.  When my code displays a message in
the minibuffer using the (message ...) syntax, I always have double
quotes around the output.  I have noticed in other packages that
messages appear without the double quotes yet the code uses the same
syntax

How do I get rid of the double quotes in the mini-buffer?

RE: message in minibuffer

[Drew Adams]

    I am a newbie in writing lisp code.  When my code displays a message in
    the minibuffer using the (message ...) syntax, I always have double
    quotes around the output.  I have noticed in other packages that
    messages appear without the double quotes yet the code uses the same
    syntax

    How do I get rid of the double quotes in the mini-buffer?

Post your code, so we can see what it does.

`message' displays a literal string argument without double-quotes. However,
if your string _contains_ double-quotes, then they will be shown by
`message', as they are characters in the string itself.

This will not display any double-quotes: (message "This is a message")

This will display double-quotes: (message "\"Quoted message\"")

If you are doing (message foo), then make sure the value of `foo' is not a
string that contains double-quotes. In particular, be aware that if you set
a string-valued variable `foo' using `set-variable' or Customize, you should
not include double-quotes in the value you enter.

Keep in mind also that the first argument to `message' is a format string.
See function `format' for the proper use of `%' in format strings. If, for
example, you use `%S' instead of `%s', then a string value will be displayed
surrounded by double-quotes. For example:

(setq foo "aaa")

(message "Here is a string value: %S." foo) ->

  Here is a string value: "aaa".

(message "Here is a string value: %s." foo) ->

  Here is a string value: aaa.

Re: message in minibuffer

[wkomornicki]

Drew:
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 minibuffer.  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?

Drew Adams wrote:
> I am a newbie in writing lisp code.  When my code displays a message in
>     the minibuffer using the (message ...) syntax, I always have double
>     quotes around the output.  I have noticed in other packages that
>     messages appear without the double quotes yet the code uses the same
>     syntax
>
>     How do I get rid of the double quotes in the mini-buffer?
>
> Post your code, so we can see what it does.
>
> `message' displays a literal string argument without double-quotes. However,
> if your string _contains_ double-quotes, then they will be shown by
> `message', as they are characters in the string itself.
>
> This will not display any double-quotes: (message "This is a message")
>
> This will display double-quotes: (message "\"Quoted message\"")
>
> If you are doing (message foo), then make sure the value of `foo' is not a
> string that contains double-quotes. In particular, be aware that if you set
> a string-valued variable `foo' using `set-variable' or Customize, you should
> not include double-quotes in the value you enter.
>
> Keep in mind also that the first argument to `message' is a format string.
> See function `format' for the proper use of `%' in format strings. If, for
> example, you use `%S' instead of `%s', then a string value will be displayed
> surrounded by double-quotes. For example:
>
> (setq foo "aaa")
>
> (message "Here is a string value: %S." foo) ->
>
>   Here is a string value: "aaa".
>
> (message "Here is a string value: %s." foo) ->
> 
>   Here is a string value: aaa.

RE: message in minibuffer

[Drew Adams]

    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.

Re: message in minibuffer

[wkomornicki]

Thanks.

That clears up a lot of other questions that I had when writing elisp
code