Making a Lua pattern case insensitive with LPeg

Question

I have an app that (among other things) supports plain-text searches and searches using Lua patterns. As a convenience, the app supports case-insensitive searches. Here is an image snippet:

The code that transforms the given Lua pattern into a case-insensitive Lua pattern isn't too pretty. It basically worries about whether or not a character is preceded by an odd or even number of escapes (%) and whether or not it is located inside of square brackets. The pattern shown in the image becomes %a[bB][bB]%%[cC][%abB%%cC]

I haven't had a chance to learn LPeg yet, and I suppose this could be my motivator.

My question is whether this is something that LPeg could have handled easily?

Answer 1

Yes, but for an easier entry into the LPeg world, consider LPeg's "re" module, which gives you a regex-like syntax and which you can specify a set of rules, as in a grammar (think Yacc, etc.). You'd basically write rules for escaped characters, bracket groups and regular characters. Then, you could associate functions to the rules, that would emit either the same text they consumed as the input or the case-insensitive modified version.

The structure of your rules would take care of the even-odd distinction automatically, bracket context, etc. LPeg uses "ordered choice", so if you add your escape rule first, it will handle %[ correctly and avoid mixing it up with the brackets rule, for example.