From: Felipe Balbi <balbif@...>
Date: 2011-04-17T04:52:16+09:00
Subject: Making a simple parser

Hi all,

To automate some of the tests I have to run, I decided to use ruby to
generate some script files on a particular (very simple) language based
on several possible input files. My first approach at this was to use
inherited method on a parent class (which I called InputFormat) to hold
all the children in an array. Then, different formats could become a
child class of InputFormat and return a known data format (I decided to
use an array of hashes because the output is really really simple) to
the output generator code.

So the idea is something like:

class InputFormat
  @children = []

  def initialize(input)
    @input = input
  end

  def parse
    @children.each { |child|
      child.parse(@input) if child.supported?(@input)
    }
  end

  def self.inherited(child)
    @children << child
  end
end

class AInputFormat < InputFormat
  def supported?
    # check if we can parse this type of file
  end

  def parse
    # parse and generate array of hashes in known format
  end
end


Then on the core file I would have something like:

input = InputFormat.new(ARGV[0])
input.parse

As it turns out, this isn't working because AInputFormat will only
inherit from InputFormat at the time I actually use it, am I right ? Any
tips you guys could give me to achieve what I want ? (from several
possible input formats generate one output format)

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