re: Regex was taking 5 days to run. So I built a tool that did it in 15 minutes. VIEW POST

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The language and what you can do with it is standardized - unions, differences, kleene stars and so on. The rest is just syntax.

Not so easy. The point is that you can't transpose a regular expression from a different language without any second thinking. It means that regular expressions are another layer of programming language that you have to take into consideration.

A well designed regex engine is a finite automata. That's it.

A computer doesn't care what a regex is. You shouldn't either, as it doesn't make any difference. The implementation can be very different and something that should be cared about.

I don't think this is too hard to read.

That's not a regular expression: it's a list of definitions used by a regex engine.

Of course you can step-by-step a RE. It's just a finite automata; just step though it.

Only if you have a library that replicate a regex engine. In many languages, you just use the regular expression engine that's natively implemented, because any non-native solution is usually several orders of magnitude slower, it's basically a reinvented wheel, and it just adds another dependency to the project.

If it's slower and takes additional configuration, the "fastest and simplest you can do" part simply disappears.

But we do have alternatives.

In some languages maybe they're worth considering. But nobody uses a custom regex engine in JavaScript, or in PHP, or in Python, except for very limited cases.

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