Add solution for exercise3-25

Author: ramsayleung

README.org

@@ -25,7 +25,7 @@
   习题完成情况:
   - 章节一: 43/46
   - 章节二: 88/97
-  - 章节三: 24/82
+  - 章节三: 25/82
   - 章节四: TODO
   - 章节五: TODO
 * 运行

chapter3/exercise3-25.rkt

@@ -0,0 +1,51 @@
+#lang racket
+
+;;; 实现与一维数组一致，差别在于 key 的表达方式，与原来使用 'a 的字符
+;;; 变量作为 key 不同，现在使用 '(a b) 列表作为 key
+(define (make-table)
+  (let ((local-table (mcons '*table* '())))
+    (define (assoc key records)
+      (cond ((null? records) false)
+            ((equal? key (mcar (mcar records)))
+             (mcar records))
+            (else (assoc key (mcdr records)))))
+
+    ;;; O(N)
+    (define (lookup key)
+      (let ((record (assoc key (mcdr local-table))))
+        (if record
+            (mcdr record)
+            false)))
+
+    (define (insert! key value)
+      (let ((record (assoc key (mcdr local-table))))
+        (if record
+            (set-mcdr! record value)
+            (set-mcdr! local-table (mcons (mcons key value) (mcdr local-table)))))
+      'ok)
+
+    (define (dispatch m)
+      (cond ((eq? m 'lookup-proc) lookup)
+            ((eq? m 'insert-proc!) insert!)
+            (else (error "Unknown operation -- TABLE" m)))
+      )
+    dispatch
+    ))
+
+(module+ test
+  (require rackunit)
+  (define op-table (make-table))
+  (define get (op-table 'lookup-proc))
+  (define put (op-table 'insert-proc!))
+
+  (test-case "Test for 1-dimentional table"
+             (put '(name) 'Alice)
+             (check-false (get '(no-exist)))
+             (check-equal? (get '(name)) 'Alice)
+             (put '(name age) 'Bob)
+             (check-equal? (get '(name age)) 'Bob)
+             (check-false (get '(age name)))
+             (put '(a b c) 'val-abc)
+             (check-equal? (get '(a b c)) 'val-abc)
+             )
+  )