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Vl-propexpr

Vl-propexpr-case

Case macro for the different kinds of vl-propexpr 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-propexpr structure, or to split into cases based on its type.

Short Form

In its short form, vl-propexpr-case allows you to safely check the type of a vl-propexpr structure. For example:

(vl-propexpr-case x :vl-propcore)

is essentially just a safer alternative to writing:

(equal (vl-propexpr-kind x) :vl-propcore)

Why is using vl-propexpr-case safer? When we directly inspect the kind with equal, there is no static checking being done to ensure that, e.g., :vl-propcore is a valid kind of vl-propexpr structure. That means there is nothing to save you if, later, you change the kind keyword for this type from :vl-propcore to something else. It also means you get no help if you just make a typo when writing the :vl-propcore 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-propexpr-case allows you to split into cases based on the kind of structure you are looking at. A typical example would be:

(vl-propexpr-case x
  :vl-propcore ...
  :vl-propinst ...
  :vl-propthen ...
  :vl-proprepeat ...
  :vl-propassign ...
  :vl-propthroughout ...
  :vl-propclock ...
  :vl-propunary ...
  :vl-propbinary ...
  :vl-propalways ...
  :vl-propeventually ...
  :vl-propaccept ...
  :vl-propnexttime ...
  :vl-propif ...
  :vl-propcase ...)

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 :vl-propcore case, you can use defprod-style foo.bar style accessors for x without having to explicitly add a vl-propcore b* binder.