how How to replace “(” with “(” in the regexp, Emacs/elisp flavor?

 

Questions


Question as title.

More specifically, I’m rather tired of having to type (, etc. every time I want a parenthesis in Emacs’s (interactive) regexp functions (not to mention the ( in code). So I wrote something like

(defadvice query-replace-regexp (before my-query-replace-regexp activate)
   (ad-set-arg 0 (replace-regexp-in-string "(" "\(" (ad-get-arg 0)))
   (ad-set-arg 0 (replace-regexp-in-string ")" "\)" (ad-get-arg 0)))))

in hope that I can conveniently forget about emacs’s idiosyncrasy in regexp during “interaction mode”. Except I cannot get the regexp right…

(replace-regexp-in-string "(" "\(" "(abc")

gives (abc instead of the wanted (abc. Other variations on the number of slashes just gives errors. Thoughts?

Since I started questioning, might as well ask another one: since lisp code is not supposed to use interactive functions, advicing query-replace-regexp should be okay, am I correct?

 

 

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Answer

The replacement you has works well for me.

Take the text:

hi there mom
hi son!

and try query-replace-regexp with your advice:

M-x query-replace-regexp (hi).*(mom) RET 1 2! RET

yields

hi mom!
hi son!

I didn’t have to put a backslash in front of the parentheses to get them to group. That said, this disables being able to match actual parentheses…

The reason the replace-regexp-in-string yields (abc, is that as a string, that is equivalent to an interactively typed (abc. In a string is used to denote that the following character is special, e.g. "t" is a string with a tab. So, in order to specify just a backslash, you need to use a backslash in front of it "" is a string containing a backslash.

Regarding advising interactive functions, lisp code can call interactive functions all it wants. A prime example is find-file – which is called all over the place. To make your advice a little safer, you can wrap the body with a check for interactive-p to avoid mussing with internal calls:

(defadvice query-replace-regexp (before my-query-replace-regexp activate)
  (when (interactive-p)
    (ad-set-arg 0 (replace-regexp-in-string "(" "\(" (ad-get-arg 0)))
    (ad-set-arg 0 (replace-regexp-in-string ")" "\)" (ad-get-arg 0)))))

elisp,emacs

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