Data commit

Task/Generic-swap/Scheme/generic-swap.ss

@@ -0,0 +1,39 @@
+; swap elements of a vector
+; vector-swap! is not part of r5rs, so we define it
+(define (vector-swap! v i j)
+(let ((a (vector-ref v i)) (b (vector-ref v j)))
+(vector-set! v i b)
+(vector-set! v j a)))
+
+(let ((vec (vector 1 2 3 4 5)))
+  (vector-swap! vec 0 4)
+  vec)
+; #(5 2 3 4 1)
+
+
+; we can swap also in lists
+(define (list-swap! v i j)
+(let* ((x (list-tail v i))
+       (y (list-tail v j))
+       (a (car x))
+       (b (car y)))
+(set-car! x b)
+(set-car! y a)))
+
+(let ((lis (list 1 2 3 4 5)))
+   (list-swap! lis 0 4)
+   lis)
+; (5 2 3 4 1)
+
+
+; using macros (will work on variables, not on vectors or lists)
+(define-syntax swap!
+(syntax-rules ()
+((_ a b)
+   (let ((tmp a))
+   (set! a b)
+   (set! b tmp)))))
+
+; try it
+(let ((a 1) (b 2)) (swap! a b) (list a b))
+; (2 1)