SICP: Exercise 1.3

Exercise 1.3

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

原始的に

(define (sum-of-squares-largest-two a b c)
  (cond ((and (<= a b) (<= b c)) (sum-of-squares b c))
        ((and (<= a c) (<= c b)) (sum-of-squares c b))
        ((and (<= b a) (<= a c)) (sum-of-squares a c))
        ((and (<= b c) (<= c a)) (sum-of-squares c a))
        ((and (<= c a) (<= a b)) (sum-of-squares a b))
        ((and (<= c b) (<= b a)) (sum-of-squares b a))))

と書いていたのだけれど、Community-Scheme-Wiki の sicp-ex-1.3 の

(define (sum-of-squares-largest-two a b c)
  (if (<= a b)
    (sum-of-squares b (if (<= a c) c a))
    (sum-of-squares a (if (<= b c) c b))))

（ちょっと変えてある）がなるほど、という解だった。手続き型の言語に慣れていると if が式であることを思い出せないんだなぁ。