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So, what is logic less mode and how do you use it? Examples are best, lets start with the basics, conditionals:

/ If the method is not false or empty?, the content will show
- article
  h1 = title

---

Inverted conditional

/ If the method is false or empty?, the content will show
-! article
  p Sorry, article not found

---

Next we'll go over resolution order.

If article.respond_to?(:title)

- article
  / Slim will execute article.send(:title)
  h1 = title

If article.respond_to?(:has_key?) and article.has_key?(:title)

- article
  / Slim will execute article[:title]
  h1 = title

If article.instance_variable_defined?(@title)

- article
  / Slim will execute article.instance_variable_get @title
  h1 = title

If all the above fails, Slim will try to resolve the title reference in the same order against the parent object. In this example, the parent would be the initial scope you are rendering the template against.

As you might have guessed, the article reference goes through the same steps against the scope.

Things to know

Instance variables are not allowed in the view code, but Slim will find and use them. Essentially, you're just using dropping the @ prefix in your template.

Parametized method calls are not allowed.

Logic less support in Rails

Install:

$ gem install slim

Require:

gem 'slim', :require => 'slim/rails'

To enable logic less mode, put this line in config/environment.rb:

Slim::Engine.set_default_options :sections => true

Logic less support in Sinatra

Sinata will have built-in support for Slim in their next release, but until then you'll need this little snippet of code:

module Sinatra
  module Templates
    def slim(template, options={}, locals={})
      render :slim, template, options, locals
    end 
  end
end

Now that's out of the way, all you have to do is require slim and set the option. This can be done in your config.ru:

require 'slim'
Slim::Engine.set_default_options :sections => true

You are then ready to rock!