Dfn: Difference between revisions

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63 bytes added ,  21:45, 10 September 2022
m
Text replacement - "</source>" to "</syntaxhighlight>"
m (Link to definition of "shy")
m (Text replacement - "</source>" to "</syntaxhighlight>")
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4
4
       3 {⍵*÷⍺} 27      ⍝ ⍺th root
       3 {⍵*÷⍺} 27      ⍝ ⍺th root
3</source>
3</syntaxhighlight>
=== Default left arguments ===
=== Default left arguments ===
Assignment to <source lang=apl inline>⍺</source> is unusual in that the entire statement is only executed if the dfn is called monadically:<ref>[https://help.dyalog.com/latest/#Language/Defined%20Functions%20and%20Operators/DynamicFunctions/Default%20Left%20Argument.htm Default Left Argument] – Dyalog APL.</ref>  
Assignment to <source lang=apl inline>⍺</syntaxhighlight> is unusual in that the entire statement is only executed if the dfn is called monadically:<ref>[https://help.dyalog.com/latest/#Language/Defined%20Functions%20and%20Operators/DynamicFunctions/Default%20Left%20Argument.htm Default Left Argument] – Dyalog APL.</ref>  
<source lang=apl>
<source lang=apl>
       root←{
       root←{
           ⍺←2          ⍝ square root by default
           ⍺←2          ⍝ square root by default
           ⍵*÷⍺          ⍝ result
           ⍵*÷⍺          ⍝ result
       }</source>
       }</syntaxhighlight>
=== Guards ===
=== Guards ===
Guards provide dfns with support for basic flow control.<ref>[https://help.dyalog.com/latest/#Language/Defined%20Functions%20and%20Operators/DynamicFunctions/Guards.htm Guards] – Dyalog APL.</ref> This is a multiline dfn with a conditional result:
Guards provide dfns with support for basic flow control.<ref>[https://help.dyalog.com/latest/#Language/Defined%20Functions%20and%20Operators/DynamicFunctions/Guards.htm Guards] – Dyalog APL.</ref> This is a multiline dfn with a conditional result:
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           ⍺=0:0        ⍝ return zero if zeroth root
           ⍺=0:0        ⍝ return zero if zeroth root
           ⍵*÷⍺          ⍝ result
           ⍵*÷⍺          ⍝ result
       }</source>
       }</syntaxhighlight>


=== Error-guards ===
=== Error-guards ===
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       Gravity 1.99e30 5.97e24 0  ⍝ trigger division by zero
       Gravity 1.99e30 5.97e24 0  ⍝ trigger division by zero
N/A
N/A
</source>
</syntaxhighlight>
=== Shy results ===
=== Shy results ===
[[Roger Hui]]'s <source lang=apl inline>assert</source> is a dfn that has become the de facto standard when it comes to test suites.<ref>Stefan Kruger. [https://www.dyalog.com/blog/2021/04/2020-problem-solving-competition-phase-ii-highlights/ 2020 Problem Solving Competition – Phase II highlights]. [[Dyalog Ltd.|Dyalog]] blog. April 30, 2021.</ref>. In it, Hui uses both a [[default left argument]] and a final assignment to make the dfn [[shy]]:
[[Roger Hui]]'s <source lang=apl inline>assert</syntaxhighlight> is a dfn that has become the de facto standard when it comes to test suites.<ref>Stefan Kruger. [https://www.dyalog.com/blog/2021/04/2020-problem-solving-competition-phase-ii-highlights/ 2020 Problem Solving Competition – Phase II highlights]. [[Dyalog Ltd.|Dyalog]] blog. April 30, 2021.</ref>. In it, Hui uses both a [[default left argument]] and a final assignment to make the dfn [[shy]]:
<source lang=apl>
<source lang=apl>
assert ← {⍺←'assertion failure' ⋄ 0∊⍵:⍺ ⎕signal 8 ⋄ shy←0}</source>
assert ← {⍺←'assertion failure' ⋄ 0∊⍵:⍺ ⎕signal 8 ⋄ shy←0}</syntaxhighlight>


== External links ==
== External links ==

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