Over
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Over (⍥
) is a primitive dyadic operator which takes two function operands and produces a derived function which pre-processes the argument(s) using the monadic right operand, before applying the left operand on/between the result(s).
Explanation
When the resulting function is used monadically, it has the same behaviour as if the Beside or Atop operator had been used:
(g ⍥ h) ⍵ |
g (h ⍵) |
When the resulting function is used dyadically, both arguments are pre-processed:
⍺ (g ⍥ h) ⍵ |
(h ⍺) g (h ⍵) |
Examples
x←3 1 2 y←4 6 5 x +⍥(⌈/) y ⍝ add the max of x and max of y 9 ⍝ same as (⌈/x)+⌈/y 9
Close composition
In SHARP APL and J, Over 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.