class Middleman::Renderers::HamlTemplate

in. So we have to resort to heavy hackery :(
thus making it impossible to pass our Middleman instance
Haml precompiles filters before the scope is even available,

def evaluate(scope, locals, &block) 

def evaluate(scope, locals, &block)
  ::Middleman::Renderers::Haml.last_haml_scope = scope
  options = @options.merge(filename: eval_file, line: line)
  @engine = ::Haml::Engine.new(data, options)
  output = @engine.render(scope, locals, &block)
  ::Middleman::Renderers::Haml.last_haml_scope = nil
  output
end

def prepare 

def prepare
end