app.rb

get '/' do

  @title = "ThePostBin - Home"

  if user_id = session[:user_id]
    @user = User.find(user_id)
  end
  haml :index
end

index.haml

%h2 Welcome.

-if session[:user_id]
  Hello #{@user.name}
-else
  %p
    Please signup

  %form{ :action => '/users/signup', :method => 'post' }
    %fieldset
      %div
        %label{ :for => "name" } Name:
        %input{ :type => "text", :name => "name" } 
      %div
        %label{ :for => "email" } Email:
        %input{ :type => "text", :name => "email" }
      %div
        %label{ :for => "password" } Password:
        %input{ :type => "password", :name => "password" }
      %input{:type => "submit", :value => "Signup", :class => "button"}

layout.haml

%html
  %head
    %title #{@title}
  %body
    -yield