Assignment

UPDATINGA GLOBAL VARIABLE

(setf *total-glasses* 0)
>(+ *total-glasses* 3)

incf decf macros

> (setf a 2)
2
> (incf a 10)
12
> (decf a)
11

The PUSH and POP Macros

push item var_stack

(pop var_stack)

when unless

== if (java)

The only advantages of WHEN and UNLESSover COND are stylistic（文体）

GENERALIZED VARIABLES

(setf x ’(jack benny was 39 for many years))
(setf (sixth x) ’several)
> x
(JACK BENNY WAS 39 FOR SEVERAL YEARS)

Lisp Toolkit: BREAK and ERROR

DIY list

use SETF on generalized variables to manipulate pointers directly

> (setf (cdr circ) circ)
(FOO FOO FOO FOO ...)

DESTRUCTIVE OPERATIONS ON LISTS

have names thatbegin with N

NCONC

a destructive version of append If the first input to NCONC is NIL, it just returns its second input

(setf x ’(a b c)) (A B C) (setf y ’(d e f)) (D E F) (append x y) Doesn’t change X or Y, but (A B C D E F) result shares structure with Y. x X is unchanged. (A B C) (nconc x y) NCONC alters the list (A B C). (A B C D E F) x X’s value has changed. (A B C D E F) y Y’s has not. (D E F)

NSUBST

a destructive version of SUBST

Other Destructive Functions

NREVERSE, NUNION, NINTERSECTION, andNSET-DIFFERENCE