Use calendar.module in my custom module I am creating a module with 2 tabs, a short term calendar and a long term calendar.
I made the tabs, but I'm already stuck..

How can I implement calendar.module to show a calendar on each tab?

This is the code of my tab:

  $items['planning/longterm'] = array(
    'title' =&gt; 'Long Term',
    'access callback' =&gt; TRUE,
    'page callback' =&gt; 'planning_page_longterm',
    'type' =&gt; MENU_LOCAL_TASK,
    'weight' =&gt; 10,
  );


In my callback function I try to call the calendar.module via this piece of code:

  if (module_exists('calendar')) {
    print theme('calendar_date_default_argument_alter', array('#item' =&gt; array('year' =&gt; '2013')));
  }
I would second the comment on trying out Views. You should be able to achieve what you want with the menu tabs and a specific calendar on that page with Views. Maybe try checking out the documentation. Without more detail in your question it is hard to say, but I'm pretty sure you don't need to make a custom module to do what you have written so far.

Also you probably should also specify which version of Drupal you are using. I'm assuming 7 but it is always better to let people know.