Efficient Evaluation of Array Subscripts of Arrays
by A. Hassitt, L. E. Lyon
The APL language allows subscripted expressions such as A[I;J;K], where A is an array and I, J and K may be scalars, vectors or arrays of any size and shape. We describe an efficient method of evaluating these expressions. The method is quite general and yet it does recognize all the special cases in which multiple subscripts can be reduced to a simpler form. We show how the same mechanism can be used to evaluate other selection operations, such as transpose, and how selection operations may be combined.