object—an object.
generalized-boolean—a generalized boolean.
Returns true if object is of type symbol
;
otherwise, returns false.
(symbolp 'elephant) → true (symbolp 12) → false (symbolp nil) → true (symbolp '()) → true (symbolp :test) → true (symbolp "hello") → false
(symbolp object) ≡ (typep object 'symbol)