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  ANSI Common Lisp   14 Conses   14.2 Dictionary of Conses

14.2.19 push Macro

Syntax:
push item place    new-place-value

Arguments and Values:
item - an object.

place - a place, the value of which may be any object.

new-place-value - a list (the new value of place).

Description:
push prepends item to the list that is stored in place, stores the resulting list in place, and returns the list.

For information about the evaluation of subforms of place, see Section 5.1.1.1 Evaluation of Subforms to Places.

Examples:
 (setq llst '(nil))  (NIL)
 (push 1 (car llst))  (1)
 llst  ((1))
 (push 1 (car llst))  (1 1)
 llst  ((1 1))
 (setq x '(a (b c) d))  (A (B C) D)
 (push 5 (cadr x))  (5 B C)  
 x  (A (5 B C) D)

Side Effects:
The contents of place are modified.

See Also:
pop, pushnew, Section 5.1 Generalized Reference

Notes:
The effect of (push item place) is equivalent to

 (setf place (cons item place))
except that the subforms of place are evaluated only once, and item is evaluated before place.

Allegro CL Implementation Details:
None.

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