Re: extending <% | %>

On Thu, 31 Jan 2008, Hans Dieter Pearcey wrote:
> On Wed, Jan 16, 2008 at 11:12:04AM -0500, Hans Dieter Pearcey wrote:
>> Attached is a patch that makes | in substitutions more powerful.
>
> The biggest problem is with using '|'.  While I think it's unlikely that anyone
> is doing lots of bitwise-or inside <% %>, it's not impossible that someone
> would write a regex that matches the pattern I'm using for finding filters; it
> is roughly:
>
>  /\| \s* \w+(\(.*\))? \s* $/x
>
> which matches, for example,
>
>  <% $x =~ m(foo|bar(baz)?) %>
>
> I can't think of a really satisfactory way to solve this.  I definitely do not
> want to get too heavily into trying to parse Perl, and the only alternative I
> can think of is to use a different delimiter for these kinds of filters.
>
> I generated a whole bunch of examples with different delimiters, and I've
> attached them, but I don't really like any of them, either, and most of them
> wouldn't completely sidestep the problem anyway.
>
> Anyone have better ideas?  I would love to hear them.

Would backslashing non-delimiting pipes be bad?

<% $x =~ m(foo\|bar(baz)?)  %>


The list of delimiters that you made
made me think that pipes could probably be generalized
to filehandles or something -- I guess that's the same
as what Otto was getting at with streams.
   You could probably easily get carried away, though.
Like I was thinking how you could pipe SQL to a database
(there's already an implicit redirection of the output
of <% %> to "out_method"), get its output, pass to whatever
formatter... but in the end, it probably would be just as easy
to do it in a <%perl> block. Note for example that something like

<% $object->expensive_method(\%args) | cache(expires_in => "10m") %>

could also be done from a <%perl> block, leaving

<% $cached_val %>

within the non-code part of the template.
   It has to fit with whatever model <% %> is meant to have,
not just be implemented because it can be. IMHO the model
for <% %> can change, but I think currently it's mainly
intended/used for outputting a variable or small expression
within a larger body of non-code, like for a quick change
of context (like how % at the beginning of a line lets
you insert a single line instead of using a block).

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