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bug#26338: 26.0.50; Collect all matches for REGEXP in current buffer


From: Philipp Stephani
Subject: bug#26338: 26.0.50; Collect all matches for REGEXP in current buffer
Date: Sat, 22 Apr 2017 19:42:15 +0000



Tino Calancha <address@hidden> schrieb am Sa., 8. Apr. 2017 um 17:20 Uhr:

>
>       Your point is about performance.
>
>
> No, I care mostly about clarity, simplicity, and good API design, including separation of concerns.
Expressibity and readability might be some kind of clarity.

Yes, but it seems we mean different things with these words. "Readability" for me means (among other things) that each logical entity has a single purpose. The single purpose of the (already way too complex) cl-loop macro is iterating over things. It doesn't concern itself with the things it should iterate over and where they come from.
 
I totally agree about API design and separation of concerns.
>  
>         I am driven by easy to write code.
>       Maybe you can provide an example about how to write those things using
>       the iter-by cl-loop clause.
>
>
> Sure:
>  (require 'generator)
> (iter-defun re-matches (regexp)
>   (while (re-search-forward regexp nil t)
>     (iter-yield (match-string 0))))
> (iter-do (m (re-matches (rx digit)))
>   (print m))
> (cl-loop for m iter-by (re-matches (rx digit))
> do (print m))
Thank you very much for your examples.  They are nice.  I am not
as familiar as you with generators.  I must study them more.

Between A) and B), the second looks at least as simple and clear as
the first one, and probably more readable.

I disagree. (A) clearly separates the generation of the stream of objects to iterate over from the iteration, (B) doesn't. (A) is extensible to any kind of iteration as long as it can be expressed using generators (or lists, vectors, ...), while for (B) you need a new keyword for every new thing to iterate over.
 

A)
(iter-defun re-matches (regexp)
   (while (re-search-forward regexp nil t)
     (iter-yield (match-string-no-properties 1))))

(cl-loop for m iter-by (re-matches "^(defun \\(\\S +\\)")
          collect m)

B)
(cl-loop for m the matches of "^(defun \\(\\S +\\)"
          collect m)

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