Re: is this behavior correct?

[Ben Kelly <ranavin@...>]

On June 14, 2011 08:46:20 AM Philippe Lhoste wrote:
> On 13/06/2011 20:59, Javier Guerra Giraldez wrote:
> > 2011/6/13 john gladkih 599133195<john@gladkih.com>:
> >> that's not standard regexp interpretation.
> > 
> > Lua patterns are not regexp
> 
> Certainly not a standard one, at least...
>
Not *any* one. Lua patterns are missing some features required to act as 
regular expressions (the grouping operator () and the alternation operator |, 
specifically), while having some additional features (%b) that let them 
describe nonregular languages!

This results in the surprising and annoying situation that with lua patterns, 
you can describe some languages that you cannot describe with regular 
expressions, but at the same time there are many regular languages that you 
cannot describe with lua patterns.

> A standard RE implementation, even if not as complete as PCRE, would
> probably be as big as full Lua code itself (including its pattern
> implementation...). And a RE engine isn't hard to plug in, you can find
> several implementations around.
> 
Every time I hear this ("a full RE implementation would be as big as Lua 
itself") it always seems to equate "full RE implementation" with PCRE, or 
POSIX EREs, or something else that starts with regular expressions and then 
adds a huge number of extra features. How big would something be that *just* 
adds () and |?

	Ben Kelly