There are actually some formats that, while not
requiring it per se ... it just really helps to know about everything ahead of time. I know it helps me in
PDF::Template to have all the data ahead of time. This is because it's a paginated format, which means I need to calculate page numbers and the like. Knowing how much more data there is allows me to calculate the final page number, so you can do things like
Page 1 / 45
and have it look right. (I'm sure there's other ways to do it, but that's what I've got so far.)
As for HTML::Template, you might want to look at HTML::Template::Expr if you want expanded functionality. Or, just take the plunge and go to Template Toolkit.
Speaking as a template author, callbacks can be ... problematic. They're not easy to write an API around. Just a few problems I have with them:
- Are all CODE references to be considered callbacks?
- Are callbacks allowed in any type of variable? Scalars are easy, but what about loop variables that need to return a hashref for the current iteration?
- What happens if a callback dies? Should I call the callback within an eval block? What do I do with $@?
- Should I allow for parameters to be passed to the callback? What is the interface within the template for that?
- Do I allow for eval within the template? How does that play with mod_perl and other persistent environments? What about safety concerns - templates are sometimes under the control of another group from the Perl developers ...
Not so simple ...
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