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