Data commit

Task/Ackermann-function/Ol/ackermann-function.ol

@@ -0,0 +1,37 @@
+; simple version
+(define (A m n)
+    (cond
+        ((= m 0) (+ n 1))
+        ((= n 0) (A (- m 1) 1))
+        (else (A (- m 1) (A m (- n 1))))))
+
+(print "simple version (A 3 6): " (A 3 6))
+
+; smart (lazy) version
+(define (ints-from n)
+   (cons* n (delay (ints-from (+ n 1)))))
+
+(define (knuth-up-arrow a n b)
+  (let loop ((n n) (b b))
+    (cond ((= b 0) 1)
+          ((= n 1) (expt a b))
+          (else    (loop (- n 1) (loop n (- b 1)))))))
+
+(define (A+ m n)
+   (define (A-stream)
+      (cons*
+         (ints-from 1) ;; m = 0
+         (ints-from 2) ;; m = 1
+         ;; m = 2
+         (lmap (lambda (n)
+                  (+ (* 2 (+ n 1)) 1))
+            (ints-from 0))
+         ;; m = 3
+         (lmap (lambda (n)
+               (- (knuth-up-arrow 2 (- m 2) (+ n 3)) 3))
+            (ints-from 0))
+         ;; m = 4...
+         (delay (ldrop (A-stream) 3))))
+   (llref (llref (A-stream) m) n))
+
+(print "extended version (A 3 6): " (A+ 3 6))