value
  k_field_principal:            0;
  k_field_rate:                 1;
  k_field_payment:              2;


procedure
  create_data_field (integer);
  create_list_box ();
  text_value_changed (integer);


object
  loan_field:   Simple_Text {
                  arguments {
                    .
                    .
                    .
                  };
                  callbacks {
                    create = procedure create_data_field (k_field_principal);
                  !  value_changed = procedure text_value_changed (k_field_principal);
                  };
                };

  Repayment_History:
                List_Box {
                  arguments {
                    .
                    .
                    .
                  };
                  callbacks { create = procedure create_list_box (); };
                };