diff --git a/TODO.md b/TODO.md
index 44ce7d8..b56e514 100644
--- a/TODO.md
+++ b/TODO.md
@@ -29,6 +29,8 @@ AST nodes should have source line numbers, it would be really nice.
 
 C backend.  Other backends (Python? Java? CIL? Scheme?)
 
+Runtime support for `str` in Ruby backend and JavaScript backend.
+
 ### Design ###
 
 Convenience:
diff --git a/eg/countdown.castile b/eg/countdown.castile
new file mode 100644
index 0000000..3b2194c
--- /dev/null
+++ b/eg/countdown.castile
@@ -0,0 +1,8 @@
+fun main() {
+  num = 10;
+  while (num > 0) {
+    print(str(num));
+    num = num - 1
+  }
+  print("Done.")
+}