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== Trains == | == Trains == | ||
A train is a series of functions in isolation. An isolated function is either surrounded by parentheses or named. | A train is a series of functions in isolation. An isolated function is either surrounded by parentheses or named. Below, <source lang=apl inline>⍺</source> and <source lang=apl inline>⍵</source> refer to the arguments of the train. <source lang=apl inline>f</source>, <source lang=apl inline>g</source>, and <source lang=apl inline>h</source> are functions (which themselves can be tacit or not), and <source lang=apl inline>A</source> is an array. The arguments are processed by the following rules: | ||
A 2-train is an ''atop'': | A 2-train is an ''atop'': | ||
<source lang=apl> | {| | ||
|<source lang=apl> (g h) ⍵</source>|| {{←→}} ||<source lang=apl>g ( h ⍵)</source> | |||
⍺ (g h) ⍵ | |- | ||
</source> | |<source lang=apl>⍺ (g h) ⍵</source>|| {{←→}} ||<source lang=apl>g (⍺ h ⍵)</source> | ||
|} | |||
A 3-train is a ''fork'': | A 3-train is a ''fork'': | ||
<source lang=apl> | {| | ||
|<source lang=apl> (f g h) ⍵</source>|| {{←→}} ||<source lang=apl>( f ⍵) g ( h ⍵)</source> | |||
⍺ (f g h) ⍵ | |- | ||
</source> | |<source lang=apl>⍺ (f g h) ⍵</source>|| {{←→}} ||<source lang=apl>(⍺ f ⍵) g (⍺ h ⍵)</source> | ||
|} | |||
The ''left tine'' of a fork can be an array: | |||
{| | |||
|<source lang=apl> (A g h)</source>|| {{←→}} ||<source lang=apl>A g ( h ⍵)</source> | |||
|- | |||
|<source lang=apl>⍺ (A g h) ⍵</source>|| {{←→}} ||<source lang=apl>A g (⍺ h ⍵)</source> | |||
|} | |||
Only [[dzaima/APL]] allows <source lang=apl inline>(A h)</source>, which it treats as <source lang=apl inline>A∘h</source>.<ref>dzaima/APL: [https://github.com/dzaima/APL/blob/ceea05e25687988ed0980a4abf4b9249b736543f/docs/differences.txt#L19 Differences from Dyalog APL]. Retrieved 09 Jan 2020.</ref> | |||
<source lang=apl> | |||
</source> | |||
== Examples == | == Examples == | ||
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=== Plus and minus === | === Plus and minus === | ||
<source lang=apl> | <source lang=apl> | ||
(+,-)2 | (+,-) 2 ⍝ ±2 | ||
2 ¯2 | 2 ¯2 | ||
5 (+,-) 2 ⍝ 5±2 | |||
7 3 | |||
</source> | </source> | ||
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</source> | </source> | ||
For a more parallel comparison of the notations, see the [[Comparison_with_traditional_mathematics#Practical_example|comparison with traditional mathematics]]. | For a more parallel comparison of the notations, see the [[Comparison_with_traditional_mathematics#Practical_example|comparison with traditional mathematics]]. | ||
== External links == | |||
== Tutorials == | |||
* Dyalog: [http://help.dyalog.com/16.0/Content/RelNotes14.0/Function%20Trains.htm version 14.0 release notes] | |||
* APL Cultivation: [https://chat.stackexchange.com/rooms/52405/conversation/lesson-23-transcribing-to-and-reading-trains Transcribing to and reading trains] | |||
* APLtrainer: [https://www.youtube.com/watch?v=kt4lMZbn-so How to read trains in Dyalog APL code] (video) | |||
* APLtrainer: [https://www.youtube.com/watch?v=A2LqqBosvY0 Function trains in APL] (video) | |||
* Dyalog Webinar: [https://www.youtube.com/watch?v=Enlh5qwwDuY?t=440 Train Spotting in Dyalog APL] (video) | |||
* Dyalog '13: [https://www.youtube.com/watch?v=7-93GzDqC08 Train Spotting in Version 14.0] (video) | |||
== Documentation == | |||
* [http://help.dyalog.com/16.0/Content/RelNotes14.0/Function%20Trains.htm Announcement] | |||
* [http://help.dyalog.com/latest/Content/Language/Introduction/Trains.htm Dyalog] | |||
==References== | |||
<references/> | |||
{{APL syntax}} | {{APL syntax}} | ||