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m (Adám Brudzewsky moved page Reverse Compose (operator) to Reverse Compose) |
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{{Built-in|Reverse Compose|⍛}}, also known as '''Before''', is a [[primitive operator]] closely related to [[ | {{Built-in|Reverse Compose|⍛}}, also known as '''Before''', is a [[primitive operator]] closely related to [[Beside]] (<source lang=apl inline>∘</source>), also known as ''After''. Called [[dyad|dyadically]] with function operands <source lang=apl inline>f</source> and <source lang=apl inline>g</source>, it uses <source lang=apl inline>f</source> [[monad|monadically]] to pre-processes the left argument before applying <source lang=apl inline>g</source> between the pre-processed left argument and the given right argument. <source lang=apl inline>X f⍛g Y</source> is thus equivalent to <source lang=apl inline>(f X) g Y</source>. The operator can be defined as the [[dop]] <source lang=apl inline>{(⍺⍺ ⍺) ⍵⍵ ⍵}</source>. Reverse compose was introduced in [[Extended Dyalog APL]], and then adopted into [[dzaima/APL]]. | ||
== Common usage == | == Common usage == | ||
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</source>{{Works in|[[dzaima/APL]], [[Extended Dyalog APL]]}} | </source>{{Works in|[[dzaima/APL]], [[Extended Dyalog APL]]}} | ||
It can also be combined with | It can also be combined with Beside to create the [[split-compose]] construct. Here, we take the [[sign]] of the left argument and apply it to the absolute value of the right argument: | ||
[https://tio.run/##SyzI0U2pSszMTfz//1Hf1EdtE4wVDq03VDA5PP1R72wg0TGj5tB6I6CYuYLh//8A Try it online!]<source lang=apl> | [https://tio.run/##SyzI0U2pSszMTfz//1Hf1EdtE4wVDq03VDA5PP1R72wg0TGj5tB6I6CYuYLh//8A Try it online!]<source lang=apl> | ||
3 ¯1 4×⍛×∘|¯2 ¯7 1 | 3 ¯1 4×⍛×∘|¯2 ¯7 1 |