change-children in area-container<%>

Takes a filter procedure and changes the container's list of non-deleted children. The filter procedure takes a list of children areas and returns a new list of children areas. The new list must consist of children that were created as subareas of this area (i.e., change-children cannot be used to change the parent of a subarea).

After the set of non-deleted children is changed, the container computes the sets of newly deleted and newly non-deleted children. Newly deleted windows are hidden. Newly non-deleted windows are shown.

Since non-window areas cannot be hidden, non-window areas cannot be deleted. If the filter procedure removes non-window subareas, an exception is raised and the set of non-deleted children is not changed.

• (send an-area-container change-children filter) -> void
     filter : procedure of one argument, a list of subarea<%> objects, that returns a list of subarea<%> objects