select

Selects or deselects a item. For selection in a single-selection list box, if a different choice is currently selected, it is automatically deselected. For selection in a multiple-selection list box, other selections are preserved, unlike set-selection.

A list 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.

The control's callback procedure is not invoked.

• (send a-list-box select n select?) -> void
      n : exact non-negative integer
      select? = #t : boolean

  If select? is #f, the item indexed by n is deselected; otherwise it is selected. List box items are indexed from 0. If n is equal to or larger than the number of choices, an exn:application:mismatch exception is raised.