Message-case
Case macro for the different kinds of message structures.
This is an ACL2::fty sum-type case macro,
typically introduced by fty::defflexsum or fty::deftagsum. It
allows you to safely check the type of a message structure, or to split
into cases based on its type.
Short Form
In its short form, message-case allows you to safely check the type of
a message structure. For example:
(message-case x :proposal)
is essentially just a safer alternative to writing:
(equal (message-kind x) :proposal)
Why is using message-case safer? When we directly inspect the
kind with equal, there is no static checking being done to
ensure that, e.g., :proposal is a valid kind of message structure. That means there is nothing to save you
if, later, you change the kind keyword for this type from :proposal to something else. It also means you get no help
if you just make a typo when writing the :proposal
symbol. Over the course of developing VL, we found that such
issues were very frequent sources of errors!
Long Form
In its longer form, message-case allows you to split into cases based
on the kind of structure you are looking at. A typical example would be:
(message-case x
:proposal ...
:endorsement ...
:certificate ...)
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 :proposal case,
you can use fty::defprod-style foo.bar style accessors for x
without having to explicitly add a proposal b*
binder.
