我先放我的stream实现
(define (stream-car stream)
(car stream))
(define (stream-cdr stream)
(force (cdr stream)))
(define (cons-stream a b)
(cons a (delay b)))
(define (list->stream lst)
(if (null? lst) '()
(cons-stream (car lst)
(list->stream (cdr lst)))))
(define (stream-foreach pred stream)
(if (null? stream)
'done
(begin
(pred (stream-car stream))
(stream-foreach pred (stream-cdr stream)))))
(define (stream-display stream)
(stream-foreach (lambda (x)
(display x)
(newline)) stream))
然后我想看看scheme能不能实现clojure中的take,range和iterate，于是
(define (stream-take n stream)
(if (or (= 0 n)
(null? stream))
'()
(cons-stream (stream-car stream)
(stream-take (1- n) (stream-cdr stream)))))
(define (stream-range start end)
(if (> start end)
'()
(cons-stream start
(stream-range (1+ start) end))))
(define (stream-iterate pred init)
(cons-stream init
(stream-iterate pred (pred init))))
测试range
(stream-display (stream-range 1 10))
1
2
3
4
5
6
7
8
9
10
done
测试take
(stream-display (stream-take 10 (stream-range 1 10)))
1
2
3
4
5
6
7
8
9
10
done
测试iterate 这里出错了
> (stream-display (stream-take 10 (stream-iterate 1+ 1)))
break> s
(time (stream-display (stream-take 10 ...)))
110 collections
1.126950969s elapsed cpu time, including 1.000801726s collecting
1.126519705s elapsed real time, including 1.000760044s collecting
922329216 bytes allocated, including 8679712 bytes reclaimed
请各位教教我 
