Decisions for "type" in APL

Authors:
W. E. Gull;M. A. Jenkins
Affiliations:
Queen's University, Kingston, Canada;Queen's University, Kingston, Canada
Venue:
POPL '79 Proceedings of the 6th ACM SIGACT-SIGPLAN symposium on Principles of programming languages
Year:
1979

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Abstract

The meaning of "type" in an APL extended to contain nested arrays is discussed. It is shown that "type" is closely related to the variety of empty arrays of the same shape and to the possible fill values needed in the "expand" and "take" functions. Choices for fill functions are systematically presented. They are classified according to the possibility of maintaining important identities involving level-manipulating functions in the case of empty arguments, to their effect on other design choices still to be made (the restriction to homogeneous arrays and the definition of the nature of basic data), and to their ability to express "type" in a natural way.