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Re: Is Elisp really that slow?

From: Emanuel Berg
Subject: Re: Is Elisp really that slow?
Date: Mon, 13 May 2019 16:23:06 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux)

Stefan Monnier wrote:

>> can this be sped up?
>>  (while (re-search-forward from nil t)
>>    (replace-match to t))
> That's a perfect example where no matter how
> many man-years you invest into a super-duper
> fancy compiler for Elisp, the above code will
> not be affected one bit, because all the time
> is normally spent within `re-search-forward`
> and `replace-match` which are already
> implemented in C.

How about this [code last]? I just wrote it.

Comments on code also welcome, as always, but
then perhaps a subject change is called for so
not to enrage anyone for being "OT" (...?).

The goal was

    - case sensitive regexp search

    - interactively, whole buffer if not
      region, otherwise region

    - from Lisp, whole buffer, if no optional
      args delimiting

What in particular will slow it down save for
the same old regexp matcher?

And how do you know what is slow and what
is fast?

And should you really think about that when you
write Elisp?


(defun case-sensitive-regexp-search-and-replace (regexp to-string &optional 
start stop)
   `(,(read-from-minibuffer "regexp: ")
     ,(read-from-minibuffer "replace: ")
     ,@(if (use-region-p) (list (region-beginning) (region-end))
         (list (point-min) (point-max))) ))
    (let ((beg (or start (point-min)))
          (end (or stop  (point-max))) )
      (goto-char beg)
      (let ((case-fold-search nil))
        (while (re-search-forward regexp end t)
          (replace-match to-string) )))))
(defalias 'cs-replace #'case-sensitive-regexp-search-and-replace)


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