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Monday, January 10, 2011

Re: [bloggerDev] Documentation on expr: ?

Heya Shumash,

We need to put together documentation on what the expr:xxx values are. Sorry about that. The front end engineers had a look over the problem you are having and gave the following insights.

The problem here is due to '%'. The current numerical expression parser is a very simple one, and doesn't support any operator precedence. So
    "post-" + data:i % 2
is the same as
    ("post-" + data:i) % 2
, which is trying to get the modulo 2 of a string and fails.

Hope that helps.

On Wed, Jan 5, 2011 at 4:01 PM, shumash <shumash@gmail.com> wrote:
I'm having a hard time understanding exactly what expressions are
supported within the expr:xxx value. What "language" are these in and
exactly what operations are supported? I have failed to find official
documentation on this, and any pointers would be appreciated.

In particular, the problem I face is trying to concatenate what I
believe to be a string to what is probably an integer in order to
create alternating styles for an array of objects, as follows:
1: <b:loop index='i' values='data:posts' var='post'>
2:   <div expr:class='&quot;post-&quot; + data:i % 2'>
3:    <b:include data='post' name='post'/>
4:  </div>
5: </b:loop>

However, this does not work: the widget within which this is located
fails to show.

Substituting line 2 with <div expr:class='&quot;post-&quot; + data:i'>
causes the code to work as expected.

What's going on? I have checked that the modulo operator is supported.
Parentheses do not fix this.

Thanks.

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Brett Morgan

Developer Programs Engineer, Blogger

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