gistfile1.builder

class MigrationManifest
  @@manifest = []
  
  def self.table(name, options = {}, &block)
    @@manifest << [:table, name, options, block]
  end
  
  def self.column(table, name, data_type, options = {})
    @@manifest << [:column, table, name, data_type, options]
  end
  
  def self.index(table, name, options = {})
    @@manifest << [:index, table, name, options]
  end
  
  def self.irreversible
    @irreversible = true
  end
  
  def self.up
    @@manifest.each do |step|
      p step
    end
  end
  
  def self.down
    raise 'Irreversible migration' if @irreversible
    
    @@manifest.reverse.each do |step|
      p step
    end
  end
end

class CreatePeople < MigrationManifest
  irreversible
  
  table :people do |t|
    t.string :name
  end
  
  column :people, :email, :string
  index :people, :email
end

CreatePeople.up
CreatePeople.down