environment - an environment object. The default is nil.

generalized-boolean - a generalized boolean.

The following kinds of forms are considered constant forms:

• Self-evaluating objects (such as numbers, characters, and the various kinds of arrays) are always considered constant forms and must be recognized as such by constantp.

• Constant variables, such as keywords, symbols defined by Common Lisp as constant (such as nil, t, and pi), and symbols declared as constant by the user in the indicated environment using defconstant are always considered constant forms and must be recognized as such by constantp.

• quote forms are always considered constant forms and must be recognized as such by constantp.

• An implementation is permitted, but not required, to detect additional constant forms. If it does, it is also permitted, but not required, to make use of information in the environment. Examples of constant forms for which constantp might or might not return true are: (sqrt pi), (+ 3 2), (length '(a b c)), and (let ((x 7)) (zerop x)).

If an implementation chooses to make use of the environment information, such actions as expanding macros or performing function inlining are permitted to be used, but not required; however, expanding compiler macros is not permitted.

 (constantp 1)  true
 (constantp 'temp)  false
 (constantp "temp))  true
 (defconstant this-is-a-constant 'never-changing)   THIS-IS-A-CONSTANT 
 (constantp 'this-is-a-constant)  true
 (constantp "temp")  true
 (setq a 6)  6 
 (constantp a)  true
 (constantp '(sin pi))  implementation-dependent
 (constantp '(car '(x)))  implementation-dependent
 (constantp '(eql x x))  implementation-dependent
 (constantp '(typep x 'nil))  implementation-dependent
 (constantp '(typep x 't))  implementation-dependent
 (constantp '(values this-is-a-constant))  implementation-dependent
 (constantp '(values 'x 'y))  implementation-dependent
 (constantp '(let ((a '(a b c))) (+ (length a) 6)))  implementation-dependent