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irasnyd@duallie lisp $ cat hw13.lisp 

;Written By: Ira Snyder

;Due Date:   03-04-2005

;Homework #: HW13 (Exercise #15a)

;;; Examples of the INC* macro input, and what it is transformed into

;

; Input:  (INC* x y z)

; Output: (progn

;           (setf z (1+ z))

;           (setf y (1+ y))

;           (setf x (1+ x))

;         )

;

; Input:  (INC* a)

; Output: (progn (setf a (1+ a)))

;

; Input:  (INC*)

; Output: (progn)

;;;

;;; The INC* macro takes an unlimited number of already initialized

;;; variables and increments them by 1. Note that variables that do not

;;; already have a value CAN NOT BE INCREMENTED.

(defmacro INC* (&rest VARS)

  (do ((VARS VARS (cdr VARS))

       (RET nil))

      ((null VARS) (cons 'progn RET))

    (setf RET (cons `(setf ,(car VARS) (1+ ,(car VARS))) RET))

  )

)

irasnyd@duallie lisp $ clisp -q

[1]> (load 'hw13.lisp)

;; Loading file hw13.lisp ...

;; Loaded file hw13.lisp

T

[2]> (setf x 0 y 1 z 3)

3

[3]> x

[4]> y

1

[5]> z

3

[6]> (INC* x y z)

1

[7]> x

1

[8]> y

2

[9]> z

4

[10]> (macroexpand-1 '(INC* x y z))

(PROGN (SETF Z (1+ Z)) (SETF Y (1+ Y)) (SETF X (1+ X))) ;

T

[11]> (setf a 0)

[12]> a

[13]> (inc* a)

1

[14]> a

1

[15]> (macroexpand-1 '(INC* a))

(PROGN (SETF A (1+ A))) ;

T

[16]> (INC*)

NIL

[17]> (macroexpand-1 '(INC*))

(PROGN) ;

T

[18]> (bye)

irasnyd@duallie lisp $