Sinatra app example

app.rb

require 'sinatra'
require 'haml'


get '/' do
  haml :index
end

get '/:name' do |n|
  @name = n
  haml :index
end

Gemfile

source :rubygems

gem 'sinatra'
gem 'haml'

index.haml

%h1= "Hello #{@name}!"

layout.haml

!!!
  %html
    %head
      %title Hello World
    %body
      = yield

O código abaixo funciona para mim.

require 'rubygems'
require 'sinatra'
require 'haml'

get '/' do
  haml :index
end

get '/:name' do |n|
  @name = n
  haml :index
end

__END__
@@layout
!!!
%html
  %head
    %title Hello World
  %body
    = yield

@@index
%h1= "Hello #{@name}!"