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  ANSI Common Lisp   5 Data and Control Flow   5.3 Dictionary of Data and Control Flow

5.3.39 constantly Function

Syntax:
constantly value    function

Arguments and Values:
value - an object.

function - a function.

Description:
constantly returns a function that accepts any number of arguments, that has no side-effects, and that always returns value.

Examples:
 (mapcar (constantly 3) '(a b c d))  (3 3 3 3)
 (defmacro with-vars (vars &body forms)
   `((lambda ,vars ,@forms) ,@(mapcar (constantly nil) vars)))
  WITH-VARS
 (macroexpand '(with-vars (a b) (setq a 3 b (* a a)) (list a b)))
 ((LAMBDA (A B) (SETQ A 3 B (* A A)) (LIST A B)) NIL NIL), true

See Also:
identity

Notes:
constantly could be defined by:

 (defun constantly (object)
   #'(lambda (&rest arguments) object))

Allegro CL Implementation Details:
None.

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