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Vl-expr

Vl-expr-case

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

Short Form

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

(vl-expr-case x :vl-literal)

is essentially just a safer alternative to writing:

(equal (vl-expr-kind x) :vl-literal)

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

(vl-expr-case x
  :vl-literal ...
  :vl-index ...
  :vl-unary ...
  :vl-binary ...
  :vl-qmark ...
  :vl-concat ...
  :vl-multiconcat ...
  :vl-bitselect-expr ...
  :vl-partselect-expr ...
  :vl-mintypmax ...
  :vl-call ...
  :vl-stream ...
  :vl-cast ...
  :vl-inside ...
  :vl-tagged ...
  :vl-pattern ...
  :vl-special ...
  :vl-eventexpr ...)

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