		Search-engine friendly clone of the ACL2 documentation.

Expr-grade

Expr-grade-case

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

Short Form

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

(expr-grade-case x :top)

is essentially just a safer alternative to writing:

(equal (expr-grade-kind x) :top)

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

Long Form

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

(expr-grade-case x
  :top ...
  :assignment ...
  :conditional ...
  :logical-or ...
  :logical-and ...
  :ior ...
  :xor ...
  :and ...
  :equality ...
  :relational ...
  :shift ...
  :additive ...
  :multiplicative ...
  :cast ...
  :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 :top case, you can use fty::defprod-style foo.bar style accessors for x without having to explicitly add a top b* binder.