Turns a regular expression into one that would work the same on a reversed string. In other words, the regex is turned to a right-to-left version of itself. This can be used to find the last (and biggest) occurrence of a regex in a string.
- Regex atoms
- Anchors: ^, $
- Single characters (called units in the program)
- Escaped characters
- Intervals
- Groups (including group operators (see after))
- Repetition operators
- Single characters: *, +, ?
- Braces-repetition, such as {2,3}
- Lazy and greedy possessive operators, such as "??" or "{2,}+"
- Group operators
- Non-capturing group: ?:
- Positive/negative lookafter: ?= / ?!
- Positive/negative lookbehind: ?<= / ?<!
To only reverse a regular expression, you can call the deep_reverse(regex) function. If you need an example on how to use a reversed regular expression, you can take a look at the find_last(regex, string) function.
This program turns:
he*llo\.to\.olle*h(?<!(micro|macro))biologisttotsigoloib(?!(orcim|orcam))^abcd{2,}?etoed{2,}?cba$
This program was made in two hours, there are bugs I have no doubt about it. What I have tested seems to work, but it would be strange if there was no problem. Moreover, I have learnt regex as an autodidact, so the vocabulary I am using may not always be the right one. The probability that anyone reads those lines is very small, but still, if you see a mistake do not hesitate to point it out to me.