Backreferences

[SonOfLilit]

[#start_line [ | '1' | [capture 1+ '11'] [1+ #repeat:1] ] #end_line]

Should compile to:

^(?:1?|(11+?)\1+)$

(which is a slight rephrasing of https://stackoverflow.com/questions/3296050/how-does-this-regex-find-primes)

[#start_line [ | '1' | [capture:factor 1+ '11'] [1+ #repeat:factor] ] #end_line]

Should compile to the same:

^(?:1?|(?P<factor>11+?)\1+)$

(because named backreferences aren't available in regex)

[capture #token][#repeat:0]1

Should compile to:

(\w*)(?:\1)1

(Wrapping required to disambiguate "\1 and then 1" from \11)

See e.g. https://learnbyexample.github.io/py_regular_expressions/groupings-and-backreferences.html

[SonOfLilit]

Python is done, Rust still needs doing