Add possibly useful utility procedures

mceval/amb-utilities.rkt

@@ -31,5 +31,23 @@
       (if (null? l) true
           (if (f (car l))
               true
-              false)))))
+              false)))
+
+    (define (length l)
+      (if (null? l)
+          0
+          (+ 1 (length (cdr l)))))
+
+    (define (list-ref list k)
+      (if (= k 0)
+          (car list)
+          (list-ref (cdr list) (- k 1))))
+
+    ;; Remove the kth element from list
+    (define (remove list k)
+      (if (= k 0)
+          (cdr list)
+          (cons (car list)
+                (remove (cdr list) (- k 1)))))
+    ))