From: George Moschovitis <gm@...>
Date: 2004-08-02T18:16:35+09:00
Subject: Macros in Ruby

Hello everyone,

one of the features of the LISP family of languages that is missing from
Ruby are macros. I think they are useful on a lot of occasions so
I would like to see Ruby support macros in the future.

However i think it is quite easy to emulate some form of macro 
functionality in Ruby. Here is some simple code:

macros.rb:
----------

$__macros__ = {}
$__required__ = {}

module Kernel

alias_method :old_require, :require
def require(path)
	return if $__required__[path]
	
	source = open(path) { |f|
		f.sysread(f.stat().size())
	}
	
	# parse macro
	source.gsub!(/defmacro\s*\/(.*?)\/\s(.*?)endmacro/m) {
		$__macros__[Regexp.new($1)] = $2 ; ""
	}
	
	# expand macros	
	$__macros__.each { |match, replace|
		source.gsub!(match, replace)
	}
	
	$__required__[path] = true

	eval(source)
end

end

require "test1.rb"
require "test2.rb"


test1.rb:
---------

defmacro /my_macro\((.*)\)/
	begin
		my_function(\1)
	rescue => ex
		puts ex
	end
endmacro

# php style foreach
defmacro /foreach\s*\((.*)\s*as(.*)\)/
	for \2 in \1
endmacro

def my_function(str)
	puts str
end

class TestClass
	def another_test
		words = %w{ simple test }
		foreach(words as word)
			puts k
		end
	end
end


test2.rb:
---------

value = "Hello World!"
my_macro(value)

numbers = [1, 2, 3, 4]

foreach (numbers as i)
	puts i
end

a = TestClass.new
a.another_test()



Once again i was suprised to find out that Ruby is so powerful!

However I would like to hear your opinion on this code. Is there any 
problem I have overlooked? Is there a better implementation? Could this 
be better designed?

If anyone finds it usefull I could create a small package with 
doc+examples and upload it to RAA.


have fun,
George Moschovitis

-- 
www.navel.gr
www.joy.gr