CLHS: Function CONSTANTLY

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Function CONSTANTLY

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

Affected By: None.

Exceptional Situations: None.

See Also:

identity

Notes:

constantly could be defined by:

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

The following X3J13 cleanup issue, not part of the specification, applies to this section:

- FUNCTION-COMPOSITION:JAN89-X3J13

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