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Add draft about Template compilation stuff

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1 parent 63994f8 commit b6d4461688ffd71c2959e6208b19239138058e69 @Whiteknight committed Feb 13, 2012
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+---
+layout: post
+categories: [Parrot, Rosella, Template]
+title: Compiling Templates
+---
+
+I had a precious few hours to myself yesterday and was able to do some updating
+work on Rosella's Template library. I was able to use the time to implement a
+feature I had wanted for a while: template compilation. You can now compile a
+template into winxed code or even compile it all the way down to a Packfile.
+Actually, that's sort of a lie. The Winxed compiler `.compile()` method returns
+an Eval PMC not a PackfileView PMC. I'm going to submit a patch for that soon,
+and when I do you'll be able to save the template to a .pbc file.
+
+Here's how to use the Template library in the basic, interpreted way:
+
+ var engine = new Rosella.Template.Engine();
+ string output = engine.generate(template, context);
+
+The template is a string with a format that I've demonstrated before, and the
+`context` is any user-defined data structure that you want to use to populate
+the variables in the template. I won't go into detail about those things in this
+post. Now, after my recent changes and additions, you can compile your template
+to an executable Sub:
+
+ var engine = new Rosella.Template.Engine();
+ var sub = engine.compile(template);
+ string output = sub(context);
+
+Or, if you really want to see the generated winxed code, you can get that:
+
+ string wx_code = engine.compile_to_winxed(template);
+
+The compilation process does take some time, there's no way to deny that. There
+are ways to mitigate that expense, of course. You can compile ahead of time and
+save the code to a file or even a .pbc and execute that later. There are several
+strategies if you're really interested, I won't go into too much detail here.
+Once the code is compiled, which can and should be done ahead of time, the time
+savings during execution are significant. Here's some benchmarking I've done
+to time a relatively simple template with a ten thousand iteration
+`<$ repeat $>` loop:
+
+ Interpreted:
+ 0.969569s - %100.000000
+ 0.796563s - %82.156419 (-%17.843581 compared to base)
+ 0.900937s - %92.921402 (-%7.078598 compared to base)
+
+ Compiled:
+ 0.365500s - %37.697161 (-%62.302839 compared to base)
+ 0.498571s - %51.421914 (-%48.578086 compared to base)
+ 0.367616s - %37.915399 (-%62.084601 compared to base)
+
+In some cases, pre-compiling the template can take a third as much time as
+interpreting the template directly. Almost every timing I've seen is around 50%
+or better of the interpreted time.
+
+This is a very new feature and I haven't added it to the test suite yet. Expect
+rough edges as I play with it and optimize it. If you're doing a lot of
+templating with Rosella, this feature could help save some time for you and plus
+it was a really fun thing to work on.

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