tasks a-s

Task/Permutations/Scheme/permutations-1.ss

@@ -0,0 +1,19 @@
+(define (insert l n e)
+  (if (= 0 n)
+      (cons e l)
+      (cons (car l)
+            (insert (cdr l) (- n 1) e))))
+
+(define (seq start end)
+  (if (= start end)
+      (list end)
+      (cons start (seq (+ start 1) end))))
+
+(define (permute l)
+  (if (null? l)
+      '(())
+      (apply append (map (lambda (p)
+                           (map (lambda (n)
+                                  (insert p n (car l)))
+                                (seq 0 (length p))))
+                         (permute (cdr l))))))