From: Michael Judge <mjudge@...>
Date: 2006-02-02T09:57:25+09:00
Subject: Grammars (mini-scripting languages)

I'm working on implementing mini-scripting languages for two different 
projects, so I'm building a framework that could handle the task 
generically.

Does this seem like a good way to approach it?
    1. Store each command's matching regular expression and ruby code 
within the database. (sample fixture below)
    2. For each line in script:
         Test line against each command's corresponding regular 
expression
         If matched, execute the command's ruby code using an 
instance_eval.

My thoughts are:
    1. Storing executable code in the database is a security problem
    2. instance_eval is slow
    3. The alternative (a big if/elsif tree) would span many pages and 
be unweildy.

Have a better suggestion?


Sample code:
	def compile
		syntax.each do |line|
			command = commands.find { |c| c.match? line }
			raise "Command not found that can process '#{line}'" if command.nil?
			instance_eval command.ruby
		end
	end


Sample commands fixture:

label:
  id: 1
  name: label
  regexp: ^Q (.*)$
  ruby: puts "$1\n"

single-punch:
  id: 2
  name: single-punch
  regexp: ^X-(\d+) (.*)$
  ruby: puts "  o $2\n"

multiple-punch:
  id: 3
  name: multiple-punch
  regexp: ^M-(\d+) (.*)$
  ruby: puts "  [ ] $2\n"

blank-line:
  id: 4
  name: blank-line
  regexp: ^\s*$
  ruby: # Do nothing

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