Emulating advanced regex features using Lua patterns and pure Lua code

[Lorenzo Donati <lorenzodonatibz@...>]

Hi all!

A recent thread about Lua patterns not being regexes induced me to start 
this thread.

I wonder if there are ways to EASILY emulate some advanced regex 
features, usually found in PCRE-like packages, without resorting to LPEG 
or C bindings to external libs.

For example, some uses of regex alternation can be emulated using 
multiple calls to string.match and using logical operators, that is:

-- sort of pseudocode
local pcre = require 'pcre'	

if pcre.match( haystack, "^foo|bar$" ) then ...

may be rewritten in pure Lua as:

if haystack:match "^foo$" or haystack:match "^bar$" then ...


Are there common Lua idioms to emulate advanced regex features as:

- Alternation (I don't know if the example above is universally applicable)
- Positive/Negative look-ahead/-behind
- Quantification/capture of complex patterns (as in pcre's "((?:foo)+)").


If there were a sort of one-to-one (almost boilerplate) translation 
between those PCRE features and Lua idioms, it would very useful.

In particular, for my typical use case, I could reuse my knowledge of 
PCRE without resorting to heavy external bindings or LPEG (I'm lazy, 
I've got little time lately and it is still on my TODO list: "learn 
LPEG" :-)


Thanks in advance for any suggestion/pointer or contribute to the 
discussion (if the list find it worthwhile :-)

Cheers.
-- Lorenzo