Add Factorial in Wren (#4386)

Author: Kaamkiya

archive/w/wren/factorial.wren

@@ -0,0 +1,26 @@
+import "os" for Process
+
+var args = Process.arguments
+
+if (args.count < 1 || args[0].count < 1) {
+  System.print("Usage: please input a non-negative integer")
+  Fiber.suspend()
+}
+
+var n = Num.fromString(args[0])
+if (n == null || n < 0) {
+  System.print("Usage: please input a non-negative integer")
+  Fiber.suspend()
+}
+
+if (n <= 1) {
+  System.print(1)
+  Fiber.suspend()
+}
+
+var res = 1
+for (i in 1..n) {
+  res = res * i
+}
+
+System.print(res)