Atop (operator): Difference between revisions

Atop was defined as subordinate to [[Over]] in [[Ken Iverson]]'s 1978 paper [[Operators and Functions]]: that is, the derived function <syntaxhighlight lang=apl inline>f¨g</syntaxhighlight> works as an Atop if <syntaxhighlight lang=apl inline>f</syntaxhighlight> is strictly monadic or (in the dyadic case) <syntaxhighlight lang=apl inline>g</syntaxhighlight> is strictly dyadic (the combined operator <syntaxhighlight lang=apl inline>¨</syntaxhighlight> was called Composition). It was added to [[SHARP APL]] as a [[close composition]] with glyph <syntaxhighlight lang=apl inline>⍥</syntaxhighlight> and name "upon" (initially "over"), with a limited implementation in 1981<ref>[https://www.jsoftware.com/papers/satn41.htm "Composition and Enclosure"]. SATN-41, 1981-06-20.</ref> followed by a full implementation in 1983 with the introduction of [[function rank]].<ref>[https://www.jsoftware.com/papers/satn45.htm "Language Extensions of May 1983"]. SATN-45, 1983-05-02.</ref> The name "Atop" was introduced by [[J]] (which uses "At" for its non-close form). The glyph <syntaxhighlight lang=apl inline>⍤</syntaxhighlight> was chosen for [[Dyalog APL 18.0]], shared with the [[Rank operator]].