b* type declaration operator.
This b* binder provides a concise syntax for type declarations,
which can sometimes improve the efficiency of Common Lisp code. See the
documentation for declare and type-spec for more information
about type declarations.
(b* (((the integer x) (form)))
is equivalent to
(let ((x (form)))
(declare (type integer x))
The the binder form only makes sense on variables, though those
variables may be prefixed with the ? or ?! to make them ignorable or
ignored. It may be nested within other binder forms.