Distance between regular expression

Question

Can we compute a sort of distance between regular expressions ?

The idea is to mesure in which way two regular expression are similar.

Answer 1

I think first you need to understand for yourself how you see a "difference" between two expressions. Basically, define a distance metric.

In general case, it would be quite different to make. Depending on what you need to do, you may see allowing one different character in some place as a big difference. In the other case, allowing any number of consequent but same characters may not yield much difference.

I'd like to emphasize as well that normally when they talk about distance functions, they apply them to..., well, let's call them, tokens. In our case, character sequences. What you are willing to do, is to apply this method not to those tokens, but to the rules a multitude of tokens will match. I'm not quite sure it even makes sense.

Still, I believe we could think of something, but not in general, but for one particular and quite restricted case. Do you have some sort of example to show us?