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constantp (Function)

— Function: constantp form &optional environment generalized-boolean
Arguments and Values:

form—a form.

environment—an environment object. The default is nil.

generalized-boolean—a generalized boolean.


Returns true if form can be determined by the implementation to be a constant form in the indicated environment; otherwise, it returns false indicating either that the form is not a constant form or that it cannot be determined whether or not form is a constant form.

The following kinds of forms are considered constant forms:

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
Affected By:

The state of the global environment (e.g., which symbols have been declared to be the names of constant variables).

See Also: