tasks a-s

Task/Power-set/Scheme/power-set-1.ss

@@ -0,0 +1,13 @@
+(define (power-set set)
+  (if (null? set)
+      '(())
+      (let ((rest (power-set (cdr set))))
+        (append (map (lambda (element) (cons (car set) element))
+                     rest)
+                rest))))
+
+(display (power-set (list 1 2 3)))
+(newline)
+
+(display (power-set (list "A" "C" "E")))
+(newline)

Task/Power-set/Scheme/power-set-2.ss

@@ -0,0 +1,23 @@
+(define (power-set lst)
+  (define (iter yield)
+    (let recur ((a '()) (b lst))
+      (if (null? b) (set! yield
+		      (call-with-current-continuation
+			(lambda (resume)
+			  (set! iter resume)
+			  (yield a))))
+	(begin (recur (append a (list (car b))) (cdr b))
+	       (recur a (cdr b)))))
+
+    ;; signal end of generation
+    (yield 'end-of-seq))
+
+  (lambda () (call-with-current-continuation iter)))
+
+(define x (power-set '(1 2 3)))
+(let loop ((a (x)))
+  (if (eq? a 'end-of-seq) #f
+    (begin
+      (display a)
+      (newline)
+      (loop (x)))))

Task/Power-set/Scheme/power-set-3.ss

@@ -0,0 +1,7 @@
+(1 2)
+(1 3)
+(1)
+(2 3)
+(2)
+(3)
+()