Rationalized APL

Rationalized APL is the name of a 1983 paper by Ken Iverson describing a backwards compatible extension to APL as developed by Iverson IBM (for example VS APL). Written following Iverson's departure from IBM to IPSA in 1980, it showcases Iverson's stance against the nested array model used by APL2 and in favor of the boxes (here, enclosed arrays) already in use by SHARP APL. It was a precursor to A Dictionary of APL and many of the ideas it introduced were later incorporated into J. It also featured the Rank operator, invented by Arthur Whitney the previous year, just prior to its inclusion in SHARP.