add more variants to the Armstrong numbers sample

samples.mlib/arms.lisp

@@ -11,12 +11,18 @@
 (require "mlib")
 
 (defmacro pr items
+  "Helper that will print each argument and then a newline."
   `(progn ,@(mapcar (lambda (it)
                       (list 'write it nil))
                     items)
           (writeln)))
 
+
+
+(pr #\Newline "Nested loops:")
+
 (defun arms ()
+  "Print all Armstrong numbers from 0 to 999."
   (let ((count 0) (abc 0))
     (dotimes (a 10)
       (dotimes (b 10)
@@ -30,9 +36,13 @@
 (time (arms))
 
 
+
+(pr #\Newline "One loop:")
+
 (defun arms2 ()
+  "Print all Armstrong numbers from 0 to 999."
   (let ((count 0))
-    (dotimes (abc 999)
+    (dotimes (abc 1000)
       (let ((a3b3c3 (+ (expt (floor abc 100) 3)
                        (expt (mod (floor abc 10) 10) 3)
                        (expt (mod abc 10) 3))))
@@ -41,3 +51,54 @@
           (pr "Armstrong number " count ": " abc))))))
 
 (time (arms2))
+
+
+
+(pr #\Newline "Using serapeum's 'summing' macro and a generator:")
+
+(defun digits (n)
+  "Return a generator (parameterless function)
+   that on subsequent invocations will return
+   the base 10 digits of 'n' from right to left."
+  (lambda ()
+    (if n
+        (values (if (< n 10)
+                    (prog1 n
+                           (setq n nil))
+                    (prog1 (mod n 10)
+                           (setq n (truncate n 10))))
+                t)
+        (values nil nil))))
+
+
+(defun armstrongp (n)
+  "Return true if 'n' is an Armstrong number."
+  (= n (summing
+         (dogenerator (n (digits n))
+           (sum (expt n 3))))))
+
+(time (let ((count 0))
+        (dotimes (n 1000)
+          (when (armstrongp n)
+            (incf count)
+            (pr "Armstrong number " count ": " n)))))
+
+
+
+(pr #\Newline "Using mapcar:")
+
+(defun armsp (n)
+  "Return true if 'n' is an Armstrong number."
+  (labels ((number->digit-list (n)
+             (string->list (format nil "%d" n)))
+           (char->number (c)
+             (- (char-code c) (char-code #\0))))
+
+    (= n (apply + (mapcar (lambda (c) (expt (char->number c) 3))
+                          (number->digit-list n))))))
+
+(time (let ((count 0))
+        (dotimes (n 1000)
+          (when (armsp n)
+            (incf count)
+            (pr "Armstrong number " count ": " n)))))