Seb's weblog

Once upon a time, I wanted to be able to generate RPN-style code from a more common Ruby-based syntax (and DSL). Fast-forward, I have been playing today with ParseTree and ruby2ruby (Thanks Ol for the hints!); The latter provides a to_sexp method on all Proc objects (which was lacking from the former). Given that a sexp is an abstract representation of a code portion, I can then use this structure to generate a new representation (in RPN, obviously) using my own “compiler”.

A real simple example (extracted from my test suite), with just an arithmetic operation:

    assert_equal "kmh,8,*", evaluate_rpn_block {
      kmh * 8
    }

The evaluate_rpn_block method calls ruby2ruby’s to_sexp and then goes through the result tree. A more complete example of what can be done:

    assert_equal "kmh,100,GT,0,kmh,IF", evaluate_rpn_block {
      if kmh > 100 then
        0
      else
        kmh
      end
    }

From there, what is lacking would be plugging the internal available functions (and operators) and matching the names used with existing definitions.

When I first started to code scripts with Ruby, one of the features that I loved was the Rexml library which made parsing XML just a breeze, most likely because I was coming from a Perl/Sax background and at the time I was surrounded by Java programmers, but also because it really is that easy to use.
At home, I have this small script that takes a XML file listing books that I have, do stuff to it and outputs more XML but in a different format and with some filtering. At first, it was ok. But recently, the source XML file got a bit hairy and larger that it used to be (just 2MB, but that’s already a bit of a constraint). So I looked around a bit, and in fact there are now a few alternatives which are faster; One of them being Hpricot which is originally an HTML parser (as I already used it earlier on) but which also works well for well-formed XML. And in fact, it isn’t much harder to use (even easier at some point) and yes, it is faster. The same script (almost) is about 7 times as fast using Hpricot rather than good ol’ Rexml. Ok, I’m convinced. (more…)

Automatic translation is nice, but please, allow it on a per-post basis instead of per-feed. kthxbye. (more…)

Single send & archive button. Grrrrrrrrreat.

This is list-matching-lines that I’m always looking after in my feeds

So they renamed their tags as folders. But they still act as tags. Don’t people get confused by the “change folders” behavior?

Downloading gmail mac notifier brings a dmg file (ok) which only contains a shell script (wt?) which opens another URL to download the notifier (W-T-F-F?!). What’s wrong with you, people, seriously?

Please, follow your gmail friends and add lab features. And add the custom colors feature, kthxbye.

Assuming that you have some way to get your source data, and that you already have followed instructions to do sparklines with JRuby and JFreeChart, you must first declare an image inside your report:

  <field name="Spark" class="net.sf.jasperreports.engine.JRRenderable"/>
[...]
  <image scaleImage="Clip" hAlign="Center" hyperlinkType="Reference">
    <reportElement x="200" y="0" width="150" height="30"/>
    <graphicElement/>
    <imageExpression class="net.sf.jasperreports.engine.JRRenderable"><![CDATA[$F{Spark}]]></imageExpression>
  </image>

And then, from JRuby, you must implement the JRDataSource interface (that is, a basic iterator over your data) to provide the corresponding field encapsulated in a JCommonDrawableRenderer:

class MySparkLine
  import "net.sf.jasperreports.engine.JRDataSource"
  include JRDataSource  
  def getFieldValue( field )
    case field.getName()
    when "Spark"
      return JCommonDrawableRenderer.new( chartObject )
    end
  end
end

And that’s as easy as it gets.

Maybe I shouldn’t trust Google spreadsheet about any kind of financial number handling.