set-empty-callbacks

Sets callbacks that are called

• when the frame group is about to become empty, and
• after the frame group is empty.

The first

• (send a-mred:frame-group set-empty-callbacks on-empty after-empty) -> void
      on-empty : a function of no arguments that returns a boolean.
      after-empty : a function of no arguments that returns void.

  The on-empty function will be called when there is one frame left in the group, and a request has been made to remove that frame from the group. If it returns #f, the operation which would have left no frames in the group is cancelled. The empty-callback defaults to a function that does no work and returns #t.

  The after-empty function is called when there are no frames left in the group. It defaults to the function void.