SICP Ex 1.3错误；语法关键字不能用作表达式：＃[keyword-value-item 13]

Question

嘿，我正在尝试写一些方案，您能帮我吗？

(define (square a b) (+ (* a a) (* b b)))

(define (sumsq x y z)
    (cond (and (< x y) (< x z) (square y z))
          (and (< y x) (< y z) (square x z))
          (else (square y z))))

(sumsq 1 2 3)

它给我一个错误;Syntactic keyword may not be used as an expression: #[keyword-value-item 13]

Answer 1

缺少两个括号。这是cond的正确语法：

(define (sumsq x y z)
    (cond ((and (< x y) (< x z)) (square y z))
          ((and (< y x) (< y z)) (square x z))
          (else (square y z))))