Re: Regex arithmetic

On Saturday, August 5, 2017 at 2:09:41 PM UTC-7, ZyX wrote:
> 2017-08-05 23:27 GMT+03:00 porphyry5 <gl00637@gmail.com>:
> > On Friday, August 4, 2017 at 10:03:16 AM UTC-7, porphyry5 wrote:
> >> :h submatch( includes
> >> Example:
> >> :s/\d\+/\=submatch(0) + 1/
> >> This finds the first number in the line and adds one to it.
> >>
> >> Needing to increment several fields consisting of underscore and a single digit (_\d) I modified the above along the lines of
> >>
> >> s/_\(\d\)/\='_'.submatch(1) + 1/gc
> >>
> >> most of which merely replaced the entire field with '1'
> >>
> >> Thinking the problem might be a conflict between the types, string and number, I tried
> >>
> >> s/_\(\d\)/\="_".nr2char(submatch(1) + 1)/gc
> >> then
> >> s/_\(\d\)/\="_".nr2char(submatch(1) + 31)/gc
> >> and finally success with
> >> s/_\(\d\)/\="_".nr2char(submatch(1) + 49)/gc
> >> which is limited to operations on just a single digit.
> >>
> >> So, is there a generally reliable method of performing arithmetic on numeric fields embedded in a larger string pattern with :s? Thank you.
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >>
> >> --
> >>
> >> Graham Lawrence
> >
> > Thank you,
> > s/_\(\d\)/\='_'.(submatch(1)+1)/g
> > works perfectly, and I see what I was trying initially
> > s/_\(\d\)/\='_'.submatch(1)+1/g
> > is actually equivalent to
> > s/_\d/\=submatch(0)+1/g
> >
> > In the meantime, I read :h substitute( and found
> > s/_\(\d\)/\=substitute(submatch(0),'\d',submatch(1)+1,'')/g
> > which avoids the problem by making a secondary pattern selection of the number alone. But that's more typing, so I will pay attention to operator precedence in future.
>
> If you write using more then one language there is a good rule: do not
> pay attention to operator precedence, just use parenthesis every time
> you are not sure. I normally just assume that precedence is "[*/%] >
> [-+] > binary comparison (>, <, >=, <=, ==, etc) > binary logical (not
> bitwise) operators (&&, ||)" which is rather safe (though there are
> languages where even these assumptions are not valid), and everything
> else needs parenthesis.
>
> >
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That's a good idea; you're saying to impose the operator precedence one needs on expressions, that it is simpler than keeping track of which particular little squiggle pre-empts another little squiggle (sorry, that's how I think of operator symbols).

It just may have a profound effect on my success rate with expressions, because, if not mathematical, my idea of precedence has been limited to "goes left to right. Thank you again.

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