tasks a-s

Task/Queue-Definition/Scheme/queue-definition-2.ss

@@ -0,0 +1,25 @@
+(define (make-queue)
+(let ((q (cons '() '())))
+(lambda (cmd . arg)
+(case cmd
+	((empty?) (null? (car q)))
+	((put) (let ((a (cons (car arg) '())))
+		(if (null? (car q))
+			(begin (set-car! q a) (set-cdr! q a))
+			(begin (set-cdr! (cdr q) a) (set-cdr! q a)))))
+	((get) (if (null? (car q)) 'empty
+		(let ((x (caar q)))
+			(set-car! q (cdar q))
+			(if (null? (car q)) (set-cdr! q '()))
+			x)))
+))))
+
+(define q (make-queue))
+(q 'put 1)
+(q 'put 6)
+(q 'get)
+; 1
+(q 'get)
+; 6
+(q 'get)
+; empty