can't get a basic shortcode to work

I can’t get my shortcode plugin to do anything – it doesn’t show the shortcode in the post itself, but it also doesn’t show anything. Here’s my most basic example.

1. created a folder “basic” in the plugins folder
2. created a file “basic.php” in the basic folder
3. activated the plugin
4. added the following code to it

5. <?php
   /*
   Plugin Name: basic
   Description: a shortcode.
   Version: 1.0
   License: GPL2
   */
   add_shortcode('basic',  function () {
   	return "the plugin has been executed";
   });
   
   add_shortcode("basic2", "basic2_handler");
   function basic2_handler() {
     $foo = "basic 2 handler";
     return $foo;
   }
   ?>

6. edited a post and added [basic] and [basic2] to the entry

the text [basic] is missing, so I am presuming that shortcodes are working (other peoples plugins work fine enough). But nothing is returned at all in its place.