tasks a-s

Task/Permutations/Scheme/permutations-3.ss

@@ -0,0 +1,11 @@
+(define (perm s)
+  (cond ((null? s) '())
+	((null? (cdr s)) (list s))
+	(else ;; extract each item in list in turn and perm the rest
+	  (let splice ((l '()) (m (car s)) (r (cdr s)))
+	    (append
+	      (map (lambda (x) (cons m x)) (perm (append l r)))
+	      (if (null? r) '()
+		(splice (cons m l) (car r) (cdr r))))))))
+
+(display (perm '(1 2 3)))