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Disambiguate with Identity element
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|<code>⊣</code> <code>⊢</code> | |<code>⊣</code> <code>⊢</code> | ||
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:''This page is about the class of primitive functions. For the result of an empty reduction, see [[Identity element]].'' | |||
An '''Identity function''', or '''tack function''', is one of the three [[primitive function]]s which returns one of its [[argument]]s with no modification: | An '''Identity function''', or '''tack function''', is one of the three [[primitive function]]s which returns one of its [[argument]]s with no modification: | ||
* '''Identity''', '''Same''', or '''Pass''' (<source lang=apl inline>⊣</source> or <source lang=apl inline>⊢</source>) is [[monadic]] and returns its only argument. | * '''Identity''', '''Same''', or '''Pass''' (<source lang=apl inline>⊣</source> or <source lang=apl inline>⊢</source>) is [[monadic]] and returns its only argument. | ||
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* '''Right Identity''', or '''Right''' (<source lang=apl inline>⊢</source>) is [[dyadic]] and returns its right argument. | * '''Right Identity''', or '''Right''' (<source lang=apl inline>⊢</source>) is [[dyadic]] and returns its right argument. | ||
The ''right tack'' glyph <source lang=apl inline>⊢</source>, when used for Right, is almost paired with Identity for the monadic case. ''Left tack'', <source lang=apl inline>⊣</source> is usually used for Identity as well, but may be given a different meaning, such as [[Stop]] in [[SHARP APL]]. | The ''right tack'' glyph <source lang=apl inline>⊢</source>, when used for Right, is almost paired with Identity for the monadic case. ''Left tack'', <source lang=apl inline>⊣</source> is usually used for Identity as well, but may be given a different meaning, such as [[Stop]] (which returns the constant <source lang=apl inline>0 0⍴0</source>) in [[SHARP APL]] and [[APLX]], or [[Hide]] (which returns the constant <source lang=apl inline>0</source> as a [[shy]] result) in [[GNU APL]]. | ||
Identity functions (Identity in particular) may be used like elements of [[APL syntax|syntax]] to break up [[stranding]], or to force a [[shy]] result to be shown. They can also be combined with an array-oriented [[operator]] to perform structural manipulations on arrays. Identity functions are a central feature of [[tacit programming]], in which functions and operators rather than names are used to direct the flow of arguments. The pairing of both Left and Right with monadic Identity makes it easier to design [[ambivalent]] functions which usefully work with one or two arguments. | Identity functions (Identity in particular) may be used like elements of [[APL syntax|syntax]] to break up [[stranding]], or to force a [[shy]] result to be shown. They can also be combined with an array-oriented [[operator]] to perform structural manipulations on arrays. Identity functions are a central feature of [[tacit programming]], in which functions and operators rather than names are used to direct the flow of arguments. The pairing of both Left and Right with monadic Identity makes it easier to design [[ambivalent]] functions which usefully work with one or two arguments. | ||
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== Uses == | == Uses == | ||
As the left [[operand]] to [[ | As the left [[operand]] to [[Beside]], Right makes the resulting [[derived function]] ignore its left argument (so the result is produced by a [[monadic]] invocation of the right operand, on the right argument). The same pattern can be produced by using Right as the right operand to [[Atop]]. | ||
<source lang=apl> | <source lang=apl> | ||
2 ⊢∘- 7 | 2 ⊢∘- 7 | ||
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1 2 3 4 5 6 | 1 2 3 4 5 6 | ||
</source> | </source> | ||
{{APL built-ins}} | |||
== External links == | |||
=== Tutorials === | |||
* Optima Systems blog: [https://optima-systems.co.uk/left-and-right-tack-in-dyalog-apl/ Left and Right Tack in Dyalog APL] | |||
=== Documentation === | |||
* Dyalog: [https://help.dyalog.com/17.1/Content/Language/Symbols/Left%20Tack.htm Left Tack], [https://help.dyalog.com/17.1/Content/Language/Symbols/Right%20Tack.htm Right Tack] | |||
* APLX: [http://microapl.com/apl_help/ch_020_020_754.htm Left], [http://microapl.com/apl_help/ch_020_020_756.htm Right], [http://microapl.com/apl_help/ch_020_020_755.htm Pass] | |||
{{APL built-ins}}[[Category:Primitive functions]] | |||