(boolean? argument) -> boolean
Tests if the given argument is explicitly a boolean value. We say "explicitly", because the boolean? primitive is an exception to the Lisp rule that states "Any value that is not #f is true." Boolean? will return true only for values of #t or #f.
Examples:
>> (boolean? 1) :: #f >> (boolean? #t) :: #t >> (define a #f) :: #f >> (boolean? a) :: #t