		Search-engine friendly clone of the ACL2 documentation.

Jexpr-rank

Jexpr-rank-case

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

Short Form

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

(jexpr-rank-case x :expression)

is essentially just a safer alternative to writing:

(equal (jexpr-rank-kind x) :expression)

Why is using jexpr-rank-case safer? When we directly inspect the kind with equal, there is no static checking being done to ensure that, e.g., :expression is a valid kind of jexpr-rank structure. That means there is nothing to save you if, later, you change the kind keyword for this type from :expression to something else. It also means you get no help if you just make a typo when writing the :expression symbol. Over the course of developing VL, we found that such issues were very frequent sources of errors!

Long Form

In its longer form, jexpr-rank-case allows you to split into cases based on the kind of structure you are looking at. A typical example would be:

(jexpr-rank-case x
  :expression ...
  :assignment ...
  :conditional ...
  :conditional-or ...
  :conditional-and ...
  :inclusive-or ...
  :exclusive-or ...
  :and ...
  :equality ...
  :relational ...
  :shift ...
  :additive ...
  :multiplicative ...
  :unary ...
  :postfix ...
  :primary ...)

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