Atop (operator)
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Atop (⍤
) is a primitive dyadic operator which takes two function operands and produces a derived function which uses the left operand monadically to post-processes the result of the ambivalent right operand.
Explanation
When the resulting function is used monadically, it has the same behaviour as if the Atop 2-train or any of the Beside or Over operators had been used:
(g ⍤ h) ⍵ |
g (h ⍵) |
When the resulting function is used dyadically, the result is post-processed:
⍺ (g ⍤ h) ⍵ |
g ⍺ h ⍵) |
Examples
x←3 1 2 y←4 6 5 x -⍤⌈ y ⍝ the negation of the max of x y ¯4 ¯6 ¯5 ⍝ same as -x⌈y ¯4 ¯6 ¯5
Close composition
In SHARP APL and J, Atop is implemented as a close composition, meaning that (using SHARP syntax) f⍥g
has the overall function rank of g
. J uses @
for the close form and @:
for the rankless form that appears in modern APLs.