Specifies that the functions named by function-names are of
the functional type type.
(declare (ftype (function (integer list) t) ith)
(ftype (function (number) float) sine cosine))
If one of the functions mentioned has a lexically apparent local definition
(as made by flet or labels), then the declaration
applies to that local definition and not to the global function definition.
ftype declarations never apply to variable bindings (see type).
The lexically apparent bindings of function-names must not be
macro definitions. (This is because ftype declares the
functional definition of each function name to be of a particular
subtype of function, and macros do not denote
can be free declarations or bound declarations.
ftype declarations of functions that appear before the body of a
form that defines that function are bound declarations.
Such declarations in other contexts are free declarations.