A case-like macro for regular expressions

:: programming, lisp

I often find myself wanting a simple case-like macro where the keys are regular expressions. regex-case is an attempt at this.

I use CL-PPCRE for the usual things regular expressions are useful for, and probably for some of the things they should not really be used for as well. I often find myself wanting a case like macro, where the keys are regular expressions. There is a contributed package for Trivia which will do this, but Trivia is pretty overwhelming. So I gave in and wrote regex-case which does what I want.

regex-case is a case-like macro. It looks like

(regex-case <thing>
  (<pattern> (...)
   <form> ...)
  (otherwise ()
   <form> ...))

Here <pattern> is a literal regular expression, either a string or in CL-PPCRE’s s-expression parse-tree syntax for them. Unlike case there can only be a single pattern per clause: allowing the parse-tree syntax makes it hard to do anything else. otherwise (which can also be t) is optional but must be last.

The second form in a clause specifies what, if any, variables to bind on a match. As an example

(regex-case line
  ("fog\\s+(.*)\\s$" (:match m :registers (v))

will bind m to the whole match and v to the substring corresponding to the first register. You can also bind match and register positions. A nice (perhaps) thing is that you can not bind some register variables:

(regex-case line
  (... (:registers (_ _ v))

will bind v to the substring corresponding to the third register. You can use nil instead of _.

The current state of regex-case is a bit preliminary: in particular I don’t like the syntax for binding thngs very much, although I can’t think of a better one. Currently therefore it’s in my collection of toys: it will probably migrate from there at some point.

Currently documentation is here and source code is here.