Re: Call macro with new root

Indeed, it's clearly not possible. This is more of a "feature request". The
suggestion of using a passed parameter won't quite solve the problem here,
because there is a fundamental inconsistency between how macros are called
from other macros and how they are called from Java.

+ When invoked from Java, you pass a "root", which _itself_ cannot be
accessed, but which provides names to the macro.
+ When invoked from a macro, you (can) pass one-or-more named objects which
can contain names & other objects.

I am using macros both directly from Java and from other macros, and I don't
want to replicate a complex set of macros to be able to accommodate both
calling conventions. This is really two or three feature requests:

1. It should be possible to invoke a macro from a macro as if it were being
invoked from Java with a given "root" value. This will facilitate
reusability of macros.
2. When invoked from Java, the "root" object itself should be available
(i.e. ${root}). This may not be useful when the root is an actual Map, but
it would be useful when the root is an actual object/bean.
3. It should be possible to invoke a top-level macro from Java with passed
parameters, if as it were being invoked by another macro. (I have no
immediate use for this, but I am sure it would be useful for someone.)

Between the three, I am most interested in #1, because I think that the
simpler a macro is, the better  -- and while having the complex
parameter-passing features is great when they're needed, I'd prefer to not
use them excessively -- particularly as the content of the macros themselves
is somewhat complicated.

Thus I can have a macro:

  <#macro Foo>...long, complicated text, coditionals, etc....
${name}...${url}...${something}...</#macro>

And then call it from Java (Where I have a wrapper around a Configuration
with an auto-import that takes a macro name and simply returns the string)
as:

  for (Widget w : widgets ) { String s = fm.macro("Library.Foo", w); ... }

And call it from within another macro (here in the same namespace):

  <#list widgets as w>
    <@Foo=w/>
  </#list>

If #2 were implemented, then I could write the somewhat uglier version: 

  <#macro Foo c>...long, complicated text, coditionals, etc....
${c.name}...${c.url}...${c.something}...</#macro>
  <#macro JavaFoo><@Foo c=${.root}</#macro>

The present implementation necessitates having the Java layer wrap the root
object in a hash, pass that, and then use the uglier macros:

  <#macro Foo c>...long, complicated text, coditionals, etc....
${c.name}...${c.url}...${c.something}...</#macro>
  <#macro JavaFoo><@Foo c=${.root}</#macro>

  Map<String,T> wrapRoot(T root) { ...return map with key "root" mapped to
the root value }

  for (Widget w : widgets ) { Map<String,Widget> wrapper = wrapRoot(w);
String s = fm.macro("Library.Foo", wrapper); ... }

The "macro" wrapper I am using could be updated do this wrapping
automatically, so the Java code could still look reasonably nice; but having
to have "Java entry point" macros and qualifier parameters would be nice to
do without.


Daniel Dekany wrote:
> 
> It's not possible to do as far as I see. Especially as it should be
lexically scoped
> (in most applications at least). The best you can do is something like:
> 
>   <#macro Product>
>     <#local c = latestProduct> <#-- c for context -->
>     ${c.name} (${c.url})
>   </#macro>
> 
> Then at least it's obvious what's going on...
 
> 
> Thursday, July 28, 2011, 9:24:14 PM, John Redford wrote:
> 
> > I want to be able to call a macro with a given node used as the
effective
> "root"
> > for the called macro.  For example, given the data model:
> >
> > (root)
> >   |
> >   +- user = "Big Joe"
> >   |
> >   +- latestProduct
> >       |
> >       +- url = "products/greenmouse.html"
> >       |
> >       +- name = "green mouse"
> >
> > I want to have these macros:
> >
> > <#macro Product>
> >  ${name} (${url})
> > </#macro>
> >
> > <#macro Describe>
> >  ${user}'s latest product is <@Product=latestProduct/>.
> > </#macro>
> >
> > Such that the result is:
> >
> > Big Joe's latest product is green mouse (products/greenmouse.html).
> >
> > I have looked into ways to achieve something like this using
> > TemplateDirectiveModel to writing a directive that re-roots the
> environment, but
> > that does not seem possible.


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