Make echo example more fun

examples/cli/echo.roc

@@ -6,9 +6,24 @@ app "echo"
 main : Task.Task {} []
 main =
     _ <- Task.await (Stdout.line "Shout into this cave and hear the echo!")
-    Task.loop {} (\{  } -> Task.map tick Step)
+    Task.loop {} (\_ -> Task.map tick Step)
 
 tick : Task.Task {} []
 tick =
     shout <- Task.await Stdin.line
-    Stdout.line shout
+    Stdout.line (echo shout)
+
+echo : Str -> Str
+echo = \shout ->
+    silence = \length ->
+        spaceInUtf8 = 32
+        List.repeat length spaceInUtf8
+    shout
+    |> Str.toUtf8
+    |> List.mapWithIndex (\i, _ ->
+        length = (List.len (Str.toUtf8 shout) - i)
+        phrase = (List.split (Str.toUtf8 shout) length).before
+        List.concat (silence (if i == 0 then 2 * length else length)) phrase)
+    |> List.join
+    |> Str.fromUtf8
+    |> Result.withDefault ""