Another very hacky proof-of-concept of template abstractions by multi-block helper functions. This time in a more concrete implementation as Rails helpers.

_box.html.haml

.box
  %h2= title
  .body= block

_column_first.html.haml

.first
  %ul
    %li The first column contains a list where the
    %li third point can be chosen freely:
    %li= block

_column_third.html.haml

.third
  %cite{:style => "color: red;"}= block

_teaser.html.haml

.teaser
  %h3 This is a teaser
  .content= block

application_helper.rb

module ApplicationHelper
  def partial_with_block(partial, block_content, locals_except_block_content={})
    concat(render(
      :partial => partial,
      :locals => locals_except_block_content.merge(:block => block_content)
    ))
  end

  def simple_content(&block)
    capture(&block)
  end

  def complex_content(type, &block)
    capture {block.call(type.new(self)).emit}
  end

  def teaser(&block)
    partial_with_block(
      'teaser',
      simple_content(&block)
    )
  end

  def box(title, &block)
    partial_with_block(
      'box',
      complex_content(Column, &block),
      {:title => title}
    )
  end

  class Column
    def initialize(ah)
      @app_helper = ah
    end

    def first(&content)
      @first = @app_helper.capture(&content)
      self
    end

    def second(&content)
      @second = @app_helper.capture(&content)
      self
    end

    def third(&content)
      @third = @app_helper.capture(&content)
      self
    end

    def emit
      @app_helper.concat(@app_helper.render(:partial => 'column_first', :locals => {:block => @first}))
      @app_helper.concat "<pre>#{@second}</pre>"
      @app_helper.concat(@app_helper.render(:partial => 'column_third', :locals => {:block => @third}))
    end
  end
end

show.html.haml

- box "The title of the box" do |col|
  - col.third do
    %p This should be a red cite in the third column.
  - col.first do
    So here I am!
  - col.second do
    Some Text that should be preformatted.

- teaser do
  %p This must be inside a teaser.