Nested RegEx

[H. S. Teoh]

On Sat, Apr 21, 2012 at 09:41:18PM +0400, Dmitry Olshansky wrote:
> On 21.04.2012 21:24, nrgyzer wrote:
> >Hi guys,
> >
> >I'm trying to use std.regex to parse a string like the following:
> >
> >string myString = "preOuter {if condition1} content1 {if condition2} content2
> >{elseif condition3} content3 {else}any other content{/if}{/if} postOuter";
> >
> 
> Simply put pure regex is incapable of arbitrary-nested if-else
> statements. In a sense if... /if is a case of balanced parens
> problem and it's widely know to form non-regular language.

This is of theoretical interest to me. Very often I find myself wanting
a concise way to express patterns with nested matching delimiters, but
regexes can't do it. But to jump to a full-blown stack-based language
seems like an overkill to me: stack languages can express *much* more
than just nested delimiters, most of which is difficult to encapsulate
in a nice, concise syntax like regexes. All I want is a simple way to
express the kind of simple nesting that matching delimiters give.


[...]
> One day I may add push-pop stack extensions (that allow this kind of
> thing) into regex but I'd have to think hard to make it efficient.
[...]

Plus, have a nice concise syntax for it (otherwise I might as well just
write a recursive descent parser for it in the first place).


T

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