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Binary-op

Binary-op-case

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

Short Form

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

(binary-op-case x :add)

is essentially just a safer alternative to writing:

(equal (binary-op-kind x) :add)

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

Long Form

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

(binary-op-case x
  :add ...
  :add.w ...
  :sub ...
  :sub.w ...
  :mul ...
  :mul.w ...
  :div ...
  :div.w ...
  :rem ...
  :rem.w ...
  :mod ...
  :pow ...
  :pow.w ...
  :shl ...
  :shl.w ...
  :shr ...
  :shr.w ...
  :and ...
  :or ...
  :xor ...
  :nand ...
  :nor ...
  :gt ...
  :gte ...
  :lt ...
  :lte ...)

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