tasks a-s

Task/Set/Scheme/set.ss

@@ -0,0 +1,43 @@
+(define (element? a lst)
+  (and (not (null? lst))
+       (or (eq? a (car lst))
+	   (element? a (cdr lst)))))
+
+; util, not strictly needed
+(define (uniq lst)
+  (if (null? lst) lst
+    (let ((a (car lst)) (b (cdr lst)))
+      (if (element? a b)
+	(uniq b)
+	(cons a (uniq b))))))
+
+(define (intersection a b)
+  (cond ((null? a) '())
+	((null? b) '())
+	(else
+	  (append (intersection (cdr a) b)
+		  (if (element? (car a) b)
+		    (list (car a))
+		    '())))))
+
+(define (union a b)
+  (if (null? a) b
+    (union (cdr a)
+	   (if (element? (car a) b)
+	     b
+	     (cons (car a) b)))))
+
+(define (diff a b) ; a - b
+  (if (null? a) '()
+    (if (element? (car a) b)
+      (diff (cdr a) b)
+      (cons (car a) (diff (cdr a) b)))))
+
+(define (subset? a b) ; A ⊆ B
+  (if (null? a) #t
+    (and (element? (car a) b)
+	 (subset? (cdr a) b))))
+
+(define (set-eq? a b)
+  (and (subset? a b)
+       (subset? b a)))