Empty arrays in extended APL

During the past several years considerable work has been done on extending APL in three areas: operators, heterogeneous data, and nested data. In each area a proposed extension must treat empty arrays consistently. In this paper various possibilities for providing consistent behavior are presented. The new proposals possess at least one of two important qualities in which older proposals tend to be deficient: consistent behavior is independent of the structural properties of rank and nesting, and the user has control over the behavior when he wants it.