LaTeX like macro for markdown

I added a macro system for my blog system. When we are used to L^aT_eX this lack can be hard to handle. Particularly when using mathematical notations. In the header of my files I simply write:

In the body it will replace every occurrence of:

• %test by Just a test,
• and %latex by L^aT_eX.

The source code is really simple. For nanoc user, simply put this file in your lib directory.

# usage:
# ---
# ...
# macros:
#   test: "passed test"
# ---
# ...
# Here is a Just a test.
#
class Macros < Nanoc3::Filter
    identifier :falacy
    attr_accessor :macro
    def initialize(arg)
        super
        @macro={}
        @macro[:tlal] = %{<span class="sc"><abbr title="Trop long à lire">tlàl</abbr> : </span>}
        @macro[:tldr] = %{<span class="sc"><abbr title="Too long; didn't read">tl;dr</abbr>: </span>}
        if @item.nil?
            if not arg.nil?
                @macro.merge!( arg )
            end
        else
            if not @item[:macros].nil?
                @macro.merge!( @item[:macros] )
            end
        end
    end
    def macro_value_for(macro_name)
        if macro_name.nil? or macro_name=="" or @macro[macro_name.intern].nil?
            return %{%#{macro_name}} 
        end
        return @macro[macro_name.intern]
    end
    def run(content, params={})
        content.gsub(/%(\w*)/) do |m| 
            if m != '%'
                macro_value_for($1)
            else
                m
            end
        end
    end
end

Macros could be very useful, read this article for example.