Convert all scheme code to racket code

Then we could leverage the toolkit provided by Racket language to test
the code.

Author: ramsayleung

chapter2/coercion.rkt

@@ -1,5 +1,6 @@
 #lang racket
 (require "generic_operation.scm")
+(require "ch2lib.scm")
 
 (define *coercion-table* (make-hash))
 

chapter2/exercise2-1.scm

@@ -1,11 +1,14 @@
+#lang racket
 ;;; 欧几里得算法求最大公约数
 (define (gcd a b)
   (if (= b 0)
       a
-      (gcb b (remainder a b))))
+      (gcd b (remainder a b))))
 
 (define (standardized-make-rat n d)
-  (let ((g (if (negative? d)- +) (gcd n d)))
+  (let* ((common-divisor (gcd n d))
+         (sign-factor (if (negative? d)- +))
+         (g (sign-factor common-divisor)))
     (cons (/ n g) (/ d g))))
 
 (define (number x)

chapter2/exercise2-17.scm

@@ -1,3 +1,4 @@
+#lang racket
 (define (list-ref items n)
   (if (= n 0)
       (car items)

chapter2/exercise2-18.scm

@@ -1,3 +1,4 @@
+#lang racket
 (define (list-ref items n)
   (if (= n 0)
       (car items)

chapter2/exercise2-20.scm

@@ -1,3 +1,4 @@
+#lang racket
 (define (append list1 list2)
   (if (null? list1)
       list2

chapter2/exercise2-21.scm

@@ -1,3 +1,4 @@
+#lang racket
 (define (square-list items)
   (if (null? items)
       (list)

chapter2/exercise2-23.scm

@@ -1,3 +1,4 @@
+#lang racket
 (define (for-each proc items)
   (let ((a (map proc items)))
     (= 1 1)))

chapter2/exercise2-26.scm

@@ -1,3 +1,4 @@
+#lang racket
 (define x (list 1 2 3))
 (define y (list 4 5 6))
 

chapter2/exercise2-27.scm

@@ -1,3 +1,4 @@
+#lang racket
 (define x (list (list 1 2) (list 3 4)))
 
 (define (append list1 list2)

chapter2/exercise2-28.scm

@@ -1,3 +1,4 @@
+#lang racket
 (define (fringe items)
   (if (not (pair? items))
       items
@@ -6,5 +7,6 @@
 	  (append (list (car items)) (fringe (cdr items))))))
 
 ;;;
+(define x (list (list 1 2) (list 3 4)))
 (fringe x) ; => (1 2 3 4)
 (fringe (list x x)) ; => (1 2 3 4 1 2 3 4)