Fix typo of interal

Author: ramsayleung

chapter3/exercise3-51.rkt

@@ -6,10 +6,10 @@
   x)
 
 
-;;; 输出 0, 因为 (stream-enumerate-interal 0 10) 会生成一组 0 - 10 的
+;;; 输出 0, 因为 (stream-enumerate-interval 0 10) 会生成一组 0 - 10 的
 ;;; 流, 而 stream-map 会把第一个流应用在 show 函数, 延时未执行的流是
 ;;; 1 - 10
-(define x (stream-map show (stream-enumerate-interal 0 10)))
+(define x (stream-map show (stream-enumerate-interval 0 10)))
 
 ;;; 输出 1 2 3 4 5，因为 stream-ref 需要递归访问 0 - 5, 因为 0 已经被
 ;;; 处理(memo-proc), 所以只会输出 1 - 5

chapter3/exercise3-52.rkt

@@ -10,7 +10,7 @@
 ;;; 返回一个 1 3 6 10 15 21 28 36 45 55 66 78 91 105 120 136 153 171
 ;;; 190 210 的流, 因为 string-enumerate-interal 会生成 1-20 的流, 然后
 ;;; accum 会累加前面的流, 然后再生成一个新的流
-(define seq (stream-map accum (stream-enumerate-interal 1 20)))
+(define seq (stream-map accum (stream-enumerate-interval 1 20)))
 
 ;;; 返回 6, 10, 28, 36, 66, 78, 120, 136, 190, 210 的流
 (define y (stream-filter even? seq))

chapter3/infinite-stream.rkt

@@ -32,8 +32,10 @@
 (define (interleave s1 s2)
   (if (stream-null? s1)
       s2
-      (cons-stream (stream-car s1)
-                   (interleave s2 (stream-cdr s1)))))
+      (if (stream-null? s2)
+          the-empty-stream
+          (cons-stream (stream-car s1)
+                       (interleave s2 (stream-cdr s1))))))
 
 (define (pairs s t)
   (if (or (stream-null? s) (stream-null? t))

chapter3/stream.rkt

@@ -65,12 +65,12 @@
                       (stream-filter pred (stream-cdr stream))))
         (else (stream-filter pred (stream-cdr stream)))))
 
-(define (stream-enumerate-interal low high)
+(define (stream-enumerate-interval low high)
   (if (> low high)
       the-empty-stream
       (cons-stream
        low
-       (stream-enumerate-interal (+ low 1) high))))
+       (stream-enumerate-interval (+ low 1) high))))
 
 ;; Testing utility functions
 (define (stream-to-list stream n)
@@ -173,8 +173,8 @@
              (check-equal? results '(5 4 3 2 1))
              )
 
-  (test-case "Test for stream-enumerate-interal"
-             (define s (stream-enumerate-interal 5 10))
+  (test-case "Test for stream-enumerate-interval"
+             (define s (stream-enumerate-interval 5 10))
              (check-equal? (stream-to-list s 10) '(5 6 7 8 9 10))
              )
   )