tasks a-s

Task/Queue-Definition/Scheme/queue-definition-1.ss

@@ -0,0 +1,15 @@
+(define (make-queue)
+  (make-vector 1 '()))
+
+(define (push a queue)
+  (vector-set! queue 0 (append (vector-ref queue 0) (list a))))
+
+(define (empty? queue)
+  (null? (vector-ref queue 0)))
+
+(define (pop queue)
+  (if (empty? queue)
+      (error "can not pop an empty queue")
+      (let ((ret (car (vector-ref queue 0))))
+        (vector-set! queue 0 (cdr (vector-ref queue 0)))
+        ret)))

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