langs a-z

Task/Anonymous-recursion/Ursala/anonymous-recursion.ursala

@@ -0,0 +1,13 @@
+#import nat
+
+fib =
+
+~&izZB?(                    # test the sign bit of the argument
+   <'fib of negative'>!%,   # throw an exception if it's negative
+   {0,1}^?<a(               # test the argument to a recursively defined function
+      ~&a,                  # if the argument was a member of {0,1}, return it
+      sum^|W(               # otherwise return the sum of two recursive calls
+         ~&,                # to the function thus defined
+         predecessor^~(     # with the respective predecessors of
+            ~&,             # the given argument
+            predecessor)))) # and the predecessor thereof