Sinatra

## Implementation

class FormBuilder
  def initialize obj, ctx
    @obj, @ctx = obj, ctx
  end
  def method_missing m, *args
    @ctx.send(m, @obj, *args)
  end
end

def form_for obj, action, &block
  haml_tag 'form', :method => 'POST', :action => action do
    haml_tag('dl') { block.call FormBuilder.new(obj, self) }
  end
end

def field_for obj, property, opts = {}
  opts = {:name => "#{obj.class.name.downcase}[#{property}]", :value => "#{obj.send(property)}"}.merge opts
  haml_tag 'dt', property.to_s.humanize
  haml_tag 'dd', :class => (obj.errors[property] ? 'error' : nil) do
    haml_tag 'input', opts
    haml_tag 'div', obj.errors[property].join("; "), :class => 'error' if obj.errors[property]
  end
end

## Usage

- form_for @new_user, '/users/create' do |f|
  = f.field_for :name, :size => 30
  = f.field_for :email, :size => 30
  = f.field_for :password, :type => 'password', :size => 15
  = f.field_for :password_confirmation, :type => 'password', :size => 15
  %button Create User