/prog/ - DERP — World4ch

Name: HERP 2010-07-22 20:53

(define (A x y)

(cond ((= y 0) 0)

((= x 0) (* 2 y))

((= y 1) 2)

(else (A (- x 1)

(A x (- y 1))))))

I understand everything up until the else.
HALP.

Name: Anonymous 2010-07-22 21:06

>>2
Read about the COND form.
Here's I'll show you an expansion of a COND form, so you'd understand how it works:



(cond ((= y 0) 0)

        ((= x 0) (* 2 y))

        ((= y 1) 2)

        (t (A (- x 1)

              (A x (- y 1)))))

=>



(if (= y 0)

    (begin 0)

    (cond ((= x 0) (* 2 y)) ((= y 1) 2) (t (a (- x 1) (a x (- y 1))))))



=>



(if (= y 0)

    (begin 0)

    (if (= x 0)

        (begin (* 2 y))

        (cond ((= y 1) 2) (t (a (- x 1) (a x (- y 1)))))))



=>



(if (= y 0)

    (begin 0)

    (if (= x 0)

        (begin (* 2 y))

        (if (= y 1)

            (begin 2)

            (cond (t (a (- x 1) (a x (- y 1))))))))



=>



(if (= y 0)

    (begin 0)

    (if (= x 0)

        (begin (* 2 y))

        (if (= y 1)

            (begin 2)

            (begin (a (- x 1) (a x (- y 1)))))))



(cond

  (test1 result1)

  ...)



=>



(if test1

    (begin result1)

    (cond ...))

DERP

1 Name: HERP 2010-07-22 20:53

9 Name: Anonymous 2010-07-22 21:06

Name: HERP 2010-07-22 20:53

Name: Anonymous 2010-07-22 21:06