# File lib/sass/tree/visitors/perform.rb, line 278
  def visit_function(node)
    env = Sass::Environment.new(@environment, node.options)

    if node.normalized_name == 'calc' || node.normalized_name == 'element' ||
        node.name == 'expression' || node.name == 'url'
      Sass::Util.sass_warn "DEPRECATION WARNING on line \#{node.line}\#{\" of \#{node.filename}\" if node.filename}:\nNaming a function \"\#{node.name}\" is disallowed and will be an error in future versions of Sass.\nThis name conflicts with an existing CSS function with special parse rules.\n"
    end

    @environment.set_local_function(node.name,
      Sass::Callable.new(node.name, node.args, node.splat, env,
                         node.children, false, "function"))
    []
  end