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<@U4714S16G> Currently there's no way to do it with `Regex` class. You can resort to `java.util.regex.Pattern` API
```
val pattern = "[0-9]+".toPattern()
val matcher = pattern.matcher(string).region(startIndex, string.length)
if (matcher.lookingAt()) { ... }
```

Thank you!!!
Now I can write my own efficient lexer without pain with hand-written finite automatons for each token class. (I know about lexer generators, but I can’t use them in my code kata)

But is there any chance that similar api will be added to the kotlin’s `Regex`?

You can have this api as an extension of Regex class, just call its `toPattern()` method and do the code above with the returned `Pattern` instance.

We could add something like that in the stdlib, but we need to investigate the use cases first to design API that suits them. Please open an issue in YouTrack (<http://kotl.in/issue|kotl.in/issue>), and describe yours.
Also it likely won't be crossplatform, 'cause JS regexps do not support such functionality.