[Wikitext-l] #If function is not computed

Hello,

I'm having problems with functions. I wrote the next code in a wiki page:

{{{#if: 0 | yes | not }}}

{{{#if: | yes | not }}}

{{#if: 0 | yes | not }}

And I get

<pre>si </pre> <pre>si </pre> <p>{{#if: 0 | si | no }} </p>

But I supposed to get "yes" in the 3th example and that functions are enclosed only with 2 parenthesis.

I have tested it in the Wikipedia and in another wiki that I have installed recently (using MediaWiki 1.16.5). ¿Why the function is not computed? ¿I need to configure some parameter in the wiki?

Thanks, Daniel