ToC DocOverview CGDoc RelNotes Index PermutedIndex
Allegro CL
Home Previous Up Next Table of Contents Index
  ANSI Common Lisp   3 Evaluation and Compilation   3.8 Dictionary Evaluation and Compilation

3.8.30 constantp 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:

Allegro CL Implementation Details:

Home Previous Up Next Table of Contents Index
© Franz Inc. 1998-2015 - File last updated 03-23-2015