pamela_example_app.rb

require 'sinatra'

get '/' do
  haml :index
end

get '/result' do
  missed_fields = params.keys.select {|key| params[key].blank? }
  haml :index and return if missed_fields

  loan_eligibility = params[:loan_length]/params[:loan_amount] + params[:income] - params[:expenses]
  haml :result
end

__END__

@@ layout
%html
  %head
    %title Terrible Loan Calculator
  %body
    = yield

@@ index
  %h1 Enter a potential customer's details and find out if they qualify for a loan!
  - if missed_fields
    %h2 Aw, shucks!
    %p Please fill in #{missed_fields.join(',')}.
  %form(method='get' action='/result')
    %input(type='text' name='loan_length' placeholder='loan_length')
    %input(type='text' name='loan_amount' placeholder='loan_amount')
    %input(type='text' name='income' placeholder='income')
    %input(type='text' name='expenses' placeholder='expenses')
    %input(type='submit' value='Determine loan eligibility')

@@ result
  %h1 Loan Eligibility: #{loan_eligibility}