2,229

edits

Jump to navigation
Jump to search

Rewrite and simplify discussion of monadic case

No edit summary |
(Rewrite and simplify discussion of monadic case) |
||

Line 1: | Line 1: | ||

{{Built-in|Reverse Compose|⍛}} | {{Built-in|Reverse Compose|⍛}} is a [[primitive operator]] closely related to [[Beside]] (<source lang=apl inline>∘</source>), which appears in [[Extended Dyalog APL]] and [[dzaima/APL]]. 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>. This dyadic definition matches the [[hook]] function Before, represented as <code>⊸</code> in [[BQN]]. | ||

Unlike Before, the [[monad]]ic case of Reverse Compose has differed across implementations. When introduced by [[Extended Dyalog APL]], <source lang=apl inline>f⍛g Y</source> evaluated to <source lang=apl inline>g Y</source>, but [[Adám Brudzewsky|Brudzewsky]]'s later Dyalog APL Vision defines<ref>[https://github.com/abrudz/dyalog_vision/blob/main/JotUnderbar.aplo JotUnderbar.aplo]</ref> it to be <source lang=apl inline>Y f g Y</source>, matching Before. This later definition might also be written <source lang=apl inline>f⍛g</source>{{←→}}<source lang=apl inline>f⍛g⍨⍨</source>{{←→}}<source lang=apl inline>g⍨∘f⍨</source>. In [[dzaima/APL]] the monadic case is simply an error. | |||

== Common usage == | == Common usage == |

Retrieved from ‘https://aplwiki.com/wiki/Special:MobileDiff/8598’