xr

Emacs has two packages called rx and xr. They allow you to write regexes in an sexp syntax and translate between that and conventional regex syntax. Furthermore you can define regex snippets and compose them into new ones. This more than anything can give you a handle on how a regex is composed. For example "\\`\\(?:[^^]\\|\\^\\(?: \\*\\|\\[\\)\\)" can be written as (: bos (| (not (in "^")) (: "^" (| " *" "[")))) Emacs also has other features to highlight matches and groups to help understand regexes better. https://www.emacswiki.org/emacs/Rx_Notation https://github.com/mattiase/xr https://www.emacswiki.org/emacs/RegularExpression

> This is really the only way to get composability with regexes If you restrict yourself to "real" regular expressions (avoid Perl extensions and such), they express regular languages[1], which do compose very well, and can be compiled into finite state machines. Regular languages are closed not only under concatenation and Kleene star, but also: - union - intersection - complement - reverse and more.[1] Real FST libraries like HFST or OpenFST let you compile and compose regular expressions this way. It's too most "standard" regex libraries stop at "re.compile" and never implement concat/intersect/complement/reverse/union. ----- For the readability issue, give rx[2] a go – you can turn plain regexes into rx syntax with xr[3] :) [1] https://en.wikipedia.org/wiki/Regular_language#Closure_prope... [2] https://www.emacswiki.o