Changing regexp to single \ for message printing

Changing regexp to single \ for message printing

[Heime]

I would like to have a function that takes a regexp such as

"\\(\\s-*\\[\\-\\] \\)\\(.*\\)"

that removes the extra \ in \\ but also add the necessary \ characters
to get another string that when used in message will print the regexp 
string with the single \.

I have tried to do the conversion myself but cannot get things quite right
with "\\(\\s-*\\\[\\\-\\\] \\\)\\\(.*\\\)\" because it is giving me

"\(\s-*M-x \-\ \)\(.*\)"

Whereas I need to get

(message regexp-display-string)

\(\s-*\[\-\] \)\(.*\)

Re: Changing regexp to single \ for message printing

[Heime]

On Saturday, July 13th, 2024 at 9:30 PM, Heime <heimeborgia@protonmail.com> wrote:

> I would like to have a function that takes a regexp such as
> 
> "\\(\\s-\\[\\-\\] \\)\\(.\\)"
> 
> that removes the extra \ in \\ but also add the necessary \ characters
> to get another string that when used in message will print the regexp
> string with the single \.
> 
> I have tried to do the conversion myself but cannot get things quite right
> with "\\(\\s-\\\[\\\-\\\] \\\)\\\(.\\\)\" because it is giving me
> 
> "\(\s-M-x \-\ \)\(.\)"
> 
> Whereas I need to get
> 
> (message regexp-display-string)
> 
> \(\s-\[\-\] \)\(.\)

For instance, consider  

( message "1. First Capturing Group \\(\\s-*\\[\\-\\]\\s-*\\)" )

It does not produce

1. First Capturing Group \(\s-*\[\-\]\s-*\)

An M-x is being introduced, and the opening [ and closing ] square brackets are
nowhere to be seen.  What is going on ?

Re: Changing regexp to single \ for message printing

[Stefan Monnier via Users list for the GNU Emacs text editor]

> ( message "1. First Capturing Group \\(\\s-*\\[\\-\\]\\s-*\\)" )

(message "%s" "1. First Capturing Group \\(\\s-*\\[\\-\\]\\s-*\\)")


        Stefan

Re: Changing regexp to single \ for message printing

[Stefan Monnier via Users list for the GNU Emacs text editor]

> I would like to have a function that takes a regexp such as
>
> "\\(\\s-*\\[\\-\\] \\)\\(.*\\)"

Nitpick, the above is the source representation of a string intended to
be used as a regexp.  The actual string (regexp) that this represents is:

    \(\s-*\[\-\] \)\(.*\)

> (message regexp-display-string)

The first argument to `message` should virtually *always* be an
immediate string rather than a reference to a variable or some
computed value.

IOW, always do

    (message "<blabla>" regexp-display-string)

unless you *really* know what you're doing and why you're doing it.


        Stefan