set-selection in radio-box%

Sets the selected radio button by position. (The control's callback procedure is not invoked.) Radio buttons are numbered from 0.

A radio box's selection can be changed by the user clicking the control, and such changes do not go through this method; use the control callback procedure (provided as an initialization argument) to monitor selection changes.

• (send a-radio-box set-selection n) -> void
     n : exact non-negative integer

  If n is equal to or larger than the number of radio buttons in the radio box, an exn:fail:contract exception is raised.