procedure:  

(apply proc arg₁ ... args) 

Proc must be a procedure and args must be a list. Calls proc with the elements of the list (append (list arg₁ ...) args) as the actual arguments.

(define (f x y z) (+ x y z)) ;等效:(f 1 2 3)(apply f '(1 2 3))(apply f 1 '(2 3))(apply f 1 2 '(3)) ;将发生错误: ;(apply f '(1) 2 3);(apply f '(1 2) 3);(apply f 1 '(2) 3)

(list arg₁ ...)部分可以省略,也可以和args合并为一个新列表.这种设置在处理不定参数的函数时非常实用.例如下面自定义imap函数模拟map的运作:

(define (imap f x . y)  (if (null? y)       (let im ((x x))         (if (null? x)             '()             (cons (f (car x)) (im (cdr x)))))       (let im ((x x) (y y))         (if (null? x)             '()             (cons (apply f (car x) (imap car y)) (im (cdr x) (imap cdr y)))))))

(apply f (car x) (imap car y))即为体现.