September Morn Update

Task/Factorial/Dylan/factorial-1.dylan

@@ -0,0 +1,7 @@
+define method factorial (n)
+  if (n < 1)
+    error("invalid argument");
+  else
+    reduce1(\*, range(from: 1, to: n))
+  end
+end method;

Task/Factorial/Dylan/factorial-2.dylan

@@ -0,0 +1,11 @@
+define method factorial (n)
+  if (n < 1)
+    error("invalid argument");
+  else
+    let total = 1;
+    for (i from n to 2 by -1)
+      total := total * i;
+    end;
+    total
+  end
+end method;

Task/Factorial/Dylan/factorial-3.dylan

@@ -0,0 +1,13 @@
+define method factorial (n)
+  if (n < 1)
+    error("invalid argument");
+  end;
+  local method loop (n)
+          if (n <= 2)
+            n
+          else
+            n * loop(n - 1)
+          end
+        end;
+  loop(n)
+end method;

Task/Factorial/Dylan/factorial-4.dylan

@@ -0,0 +1,16 @@
+define method factorial (n)
+  if (n < 1)
+    error("invalid argument");
+  end;
+  // Dylan implementations are required to perform tail call optimization so
+  // this is equivalent to iteration.
+  local method loop (n, total)
+          if (n <= 2)
+            total
+          else
+            let next = n - 1;
+            loop(next, total * next)
+          end
+        end;
+  loop(n, n)
+end method;

Task/Factorial/Dylan/factorial.dylan

@@ -1,3 +0,0 @@
-define method factorial(n)
-  reduce1(\*, range(from: 1, to: n));
-end