I'm trying to write a scheme function that does the following (taken from SICP):

Exercise 1.3. Define a procedure that takes three numbers as arguments and returns the sum of the squares of the two larger numbers.

Here's my attempt:

(define (square-sum-larger a b c)
  (cond ((and (< a b) (< a c))) (  (* b b) (* c c)))
  (cond ((and (< b c) (< b a))) (  (* a a) (* c c)))
  (cond ((and (< c a) (< c b))) (  (* b b) (* a a)))
)

When I enter this into the biwa scheme interpreter, I get the following:

(square-sum-larger 4 5 6)
16

Since 4 is less than 5 and 6, shouldn't the first condition be evaluated, meaning that the sum of the squares of 5 and 6 should be returned?

CodePudding user response：

(define (square-sum-larger a b c)
  (cond ((and (< a b) (< a c))) (  (* b b) (* c c))) ;; this is thrown away
  (cond ((and (< b c) (< b a))) (  (* a a) (* c c))) ;; this is thrown away
  (cond ((and (< c a) (< c b))) (  (* b b) (* a a)))
)

Only the last of the three cond does anything useful; the previous cond expressions do not have any side effect, since they perform only calculations, and their value is not used. The are dead code which a Scheme compiler can eliminate entirely.

You probably wanted to combine all of the clauses into a single cond:

(define (square-sum-larger a b c)
  (cond ((and (< a b) (< a c))) (  (* b b) (* c c))
        ((and (< b c) (< b a))) (  (* a a) (* c c))
        ((and (< c a) (< c b))) (  (* b b) (* a a))))