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