用scheme重写Python的三大函数map reduce 和filter

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

(map + '(1 2 3) '(1 2 3) '(1 2 3))
(imap + '(1 2 3) '(1 2 3) '(1 2 3))

(define (filter f x)
(let recur ((x x))
(if (null? x)
'()
(if (f (car x))
(cons (car x) (recur (cdr x)))
(recur (cdr x))))))

(filter even? '(1 2 3 4 5))

(define (reduce f x . ini)
(if (null? ini)
(let recur ((res (f (car x) (cadr x)))(x (cddr x)))
(if (null? x)
res
(recur (f res (car x)) (cdr x))))
(reduce f (cons (car ini) x))))

(reduce + '(1 2 3 4))
(reduce + '(1 2 3 4) 10)
(reduce * '(1 2 3 4))
(reduce * '(1 2 3 4) 10)

(3 6 9)
(3 6 9)
(2 4)
10
20
24
240
>