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bug#19208: replace-match unhelpful error message


From: Lars Ingebrigtsen
Subject: bug#19208: replace-match unhelpful error message
Date: Sat, 03 Aug 2019 22:31:17 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

Paul Eggert <address@hidden> writes:

>> No, that's just another sanity check -- num_regs is the max allowed
>> number of sub-matches.  (I've now added some comments to clarify.)
>
> Unfortunately that patch messes up the sanity check, as the patched
> code allows 'sub' to be negative, or to be equal to
> search_regs.num_regs, and in either case this results in a bad
> pointer.

Sorry; thanks for fixing.

>> Yoda conditionals and a !...
>
> Actually those were Leibniz conditionals, which are comparisons
> involving "<" or "<=". The idea is that the conditionals' textual
> order reflects numeric order. This is a common style in math when
> doing range checking, e.g., "0 <= i < n". Yoda conditionals are
> expressions like "0 != x" which I agree are confusing.

Well, I think both are called Yoda conditionals, and they are
demonstrably confusing for people not used to seeing conditionals
written that way, which is I think pretty much everybody, except four
people working on Emacs.  :-)

In real life, nobody says "if 62 is less than your age, you're eligible
for Medicare".  I think one should write code for legibility -- but
opinions on what's legible various, of course.  Reading "if (62 < age)",
for me, requires mental gymnastics.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no





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