Regex-case
Case macro for the different kinds of regex structures.
This is an ACL2::fty sum-type case macro,
typically introduced by fty::defflexsum or deftagsum. It
allows you to safely check the type of a regex structure, or to split
into cases based on its type.
Short Form
In its short form, regex-case allows you to safely check the type of
a regex structure. For example:
(regex-case x :exact)
is essentially just a safer alternative to writing:
(equal (regex-kind x) :exact)
Why is using regex-case safer? When we directly inspect the
kind with equal, there is no static checking being done to
ensure that, e.g., :exact is a valid kind of regex structure. That means there is nothing to save you
if, later, you change the kind keyword for this type from :exact to something else. It also means you get no help
if you just make a typo when writing the :exact
symbol. Over the course of developing VL, we found that such
issues were very frequent sources of errors!
Long Form
In its longer form, regex-case allows you to split into cases based
on the kind of structure you are looking at. A typical example would be:
(regex-case x
:exact ...
:repeat ...
:concat ...
:disjunct ...
:charset ...
:start ...
:end ...
:group ...
:backref ...
:reverse-pref ...
:no-backtrack ...
:case-sens ...
:zerolength ...)
It is also possible to consolidate ``uninteresting'' cases using
:otherwise.
For convenience, the case macro automatically binds the fields of x for
you, as appropriate for each case. That is, in the :exact case,
you can use defprod-style foo.bar style accessors for x
without having to explicitly add a exact b*
binder.
