[Zope-CMF] how do I use returned value

[Agata Cruickshank]

I have a page in CMF which displays text from another page:

<dtml-with body_pages>            
 <dtml-var "testpage.CookedBody()">
</dtml-with>

That works fine, but I don't want to hardcode 'testpage' and would like it to be the id of the host page. However, the code below doesn't work.(the host page id is testpage and there is a testpage in body_pages folder)

<dtml-let result="getId()">
<dtml-with body_pages>            
  <dtml-var "result.CookedBody()">
</dtml-with>
</dtml-let>

How can I push result value to the CookedBody method?

Many thanks for any code snippets.
Agata