def contract_reader(meth_to_clause)
      attr_reader(*(meth_to_clause.keys))
      meth_to_clause.each do |meth, cls|
        contract meth, nil => cls
      end
    end
def contract_reader(meth_to_clause)
      attr_reader(*(meth_to_clause.keys))
      meth_to_clause.each do |meth, cls|
        contract meth, nil => cls
      end
    end
Defines contract-checked attribute readers with the given hash of method
 name to clause.