seaofclouds/custom_error_message.rb

## custom_error_message.rb
error do
  @e = request.env['sinatra_error']
  haml :"error"
end

get "/:name" do
  @tag    = Tag.first(:name => params[:name]) || raise('Tag not found')
  haml :list
end

## error.haml
%h1= @e
	error do
	@e = request.env['sinatra_error']
	haml :"error"
	end

	get "/:name" do
	@tag = Tag.first(:name => params[:name]) \|\| raise('Tag not found')
	haml :list
	end