
ANSI Common Lisp 25 Environment 25.2 Dictionary of Environment
25.2.21 +, ++, +++ 
Variable 
 Value Type:

an object.
 Initial Value:

implementationdependent.
 Description:

The variables +, ++, and +++ are maintained by the
Lisp readevalprint loop to save forms that were
recently evaluated.
The value of + is the last form that was evaluated,
the value of ++ is the previous value of +, and
the value of +++ is the previous value of ++.
 Examples:

(+ 0 1) 1
( 4 2) 2
(/ 9 3) 3
(list + ++ +++) ((/ 9 3) ( 4 2) (+ 0 1))
(setq a 1 b 2 c 3 d (list a b c)) (1 2 3)
(setq a 4 b 5 c 6 d (list a b c)) (4 5 6)
(list a b c) (4 5 6)
(eval +++) (1 2 3)
#.`(,@++ d) (1 2 3 (1 2 3))
 Affected By:

Lisp readevalprint loop.
 See Also:

 (variable),
* (variable),
/ (variable),
Section 25.1.1 Top level loop
 Allegro CL Implementation Details:

None.
