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

There are a few of metrics you could use:

1. The length of a valid match. Some regexs have a fixed size, some an upper limit and some a lower limit. Compare how similar their lengths or possible lengths are.

2. The characters that match. Any regex will have a set of characters a match can contain (maybe all characters). Compare the set of included characters.

3. Use a large document and see how many matches each regex makes and how many of those are identical.

Are you looking for strict equivalence?