		Search-engine friendly clone of the ACL2 documentation.

Tyspecseq

Tyspecseq-case

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

Short Form

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

(tyspecseq-case x :void)

is essentially just a safer alternative to writing:

(equal (tyspecseq-kind x) :void)

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

Long Form

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

(tyspecseq-case x
  :void ...
  :char ...
  :schar ...
  :uchar ...
  :sshort ...
  :ushort ...
  :sint ...
  :uint ...
  :slong ...
  :ulong ...
  :sllong ...
  :ullong ...
  :bool ...
  :float ...
  :double ...
  :ldouble ...
  :struct ...
  :union ...
  :enum ...
  :typedef ...)

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