Re: Missing SRE component in BNF

[Alex Shinn <alexshinn@xxxxxxxxx>]

On Thu, Jul 3, 2014 at 4:19 AM, Takashi Kato <ktakashi@xxxxxxxxx> wrote:

Hi there,

In SRE Syntax section, there are bunch of missing items in BNF but
described in below section. Following items are missing. (Not sure
if these are complete set, though.)

- English names of 'Repeating patterns'
- backref
- English names of 'Non-Greedy Patterns'

Followings are charset

- char-range
- complement
- difference

Thanks!  I've added these, as well as char-set.

The BNF was also missing enclosing < > in some cases.

BTW, why do 'look-ahead', 'look-behind', 'neg-look-ahead' and 'neg-look-
behind' not have short name like '?=', '?!', '?<-' and '?<!'? Not sure
how often these are used but it might be convenient to have short names.

I think frequency of use is key here.  : occurs in most

SREs so is worth shortening.  * is also super-common,

actually _is_ its name (the Kleene star) and occurs in

other notation like BNFs, so I think the short name is

preferable.  Likewise ? and + are very common and also

used in other notation.

Perl's ?... extensions were chosen because they ran out

of special characters, so are somewhat harder to remember.

Plus (depending on style) they're not used that often.  Unless

others speak up in favor of short names I'll keep them to

long names only.

-- 

Alex