test：增加 Demo9

playground/Demo9/Main.snow

@@ -0,0 +1,31 @@
+module: Math
+    function: main
+        parameter:
+        return_type: int
+        body:
+            Math.factorial(6)
+            return 0
+        end body
+    end function
+
+    function: factorial
+        parameter:
+            declare n:int
+        return_type: int
+        body:
+            declare num1:int = 1
+            loop:
+                initializer:
+                    declare counter:int = 1
+                condition:
+                    counter <= n
+                update:
+                    counter = counter + 1
+                body:
+                    num1 = num1 * counter
+                end body
+            end loop
+            return num1
+        end body
+    end function
+end module