Re: macro errors

Wednesday, July 25, 2012, 6:09:00 AM, Sam Steingold wrote:

> Hi,
> I am getting various macro errors:
>
> <#macro sentiment scmr model><#if scmr??>
>   <#assign senti = "${scmr.results[model]}">
>     <#if senti??>
>       <td>${senti} ---- ${senti.sentimentType}</td>
>       <td>${senti.score?html}</td>
>     <#else><td align="center" colspan="2">none</td>
>     </#if>
> </#if></#macro>
>
> first error:
>
> POSITIVE(1.0/1) ---- Expected hash. senti evaluated instead to freemarker.template.SimpleScalar
>
> this is coming from "${senti} ---- ${senti.sentimentType}"
> apparently, "senti" is the string representation of the object,
> not the object itself.
> how do I fix that?
>
> second error:
>
> Error executing macro: sentiment required parameter: scmr is not specified.
>
> this is coming from this invocation:
>
>  <@sentiment model=model scmr=result.title/>
>
> here `result' is non-null, but result.title is null.
> I do check for that in the macro, but, apparently, it has to be done
> outside.  Why?

Yeah, the null-madness from the dark ages of FreeMarker, here to stay
with us as far as backward compatibility is kept. Basically, it's
suspected by FreeMarker that the expression result.title is a typo,
and that's why it's undefined (null), hence the error. Now, maybe it's
defined, like `result` is a JavaBean where you have a getTitle()
method that returns null, but FreeMarker doesn't differentiate,
because, if `result` is a Map on the Java-side and there's no title
then there's indeed no "title" key (hence it can't be told if
result.title is a typo or just Java-null). Surely you could tell that
if `result` is a JavaBean, but you should be to able to switch
back-and-forth between a JavaBean `result` and a Map `result` in the
data-model without changing (breaking) the behavior of templates, so
you get the common subset.

What to do? Here's a hack... If know that result.title should be a
String or null, you can call the macro as (note the "!"):

  <@sentiment model=model scmr=result.title! />

Then in the macro you can do <#if a?is_sequence>title was null</#if>
or such.

There's also an old implementation bug (that's kept for
backward-compatibility), where, if you pass an undefined expression to
a macro as a parameter (like even something that's indeed a typo), and
the macro defines a default value for the parameter, that default
value will kick in. So if you prefer, you can just do this:

  <#macro sentiment scmr! model><#if scmr?is_sequence>

and then you don't need the `!` when calling the macro.

BTW, instead of `?is_sequence` you could use `== ''` too, however if
the parameter can be legally an empty string then it's not a generic
solution.

> Thanks!

-- 
Best regards,
 Daniel Dekany


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