solutions to 4.38, 4.39 and 4.40

[sicp.git] / src / sicp / ch2_3.rkt

diff --git a/src/sicp/ch2_3.rkt b/src/sicp/ch2_3.rkt
index 45157585e7ef1d44f78c47019b8f90b3ff92372d..81e4dadabf30901bb83f9a174c34e06540c45839 100644 (file)
--- a/src/sicp/ch2_3.rkt
+++ b/src/sicp/ch2_3.rkt
@@ -1,5 +1,10 @@
 #lang racket
 
+(define (memq item x)
+  (cond ((null? x) #f)
+        ((eq? item (car x)) x)
+        (else (memq item (cdr x)))))
+
 ;; leaf nodes
 (define (make-leaf leaf weight)
   (list 'leaf leaf weight))
@@ -70,4 +75,13 @@
                                (cadr pair))
                     (make-leaf-set (cdr pairs))))))
 
-(provide make-code-tree make-leaf decode leaf? symbol-leaf left-branch right-branch symbols)
\ No newline at end of file
+(provide make-code-tree 
+         make-leaf 
+         decode 
+         leaf? 
+         symbol-leaf 
+         left-branch 
+         right-branch 
+         symbols 
+         make-leaf-set 
+         adjoin-set)
\ No newline at end of file