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{{Built-in|Constant|⍨}} is a [[monadic operator]] which takes an [[array]] as its [[operand]] and becomes a [[function]] which returns the operand array regardless of its [[argument|arguments]]. It was first introduced in [[Extended Dyalog APL]], sharing its [[glyph]] with [[Commute]], and was adopted in [[Dyalog APL 18.0]] as an alternative to the constant [[dfn]] such as <source lang=apl inline>{0}</ | {{Built-in|Constant|⍨}} is a [[monadic operator]] which takes an [[array]] as its [[operand]] and becomes a [[function]] which returns the operand array regardless of its [[argument|arguments]]. It was first introduced in [[Extended Dyalog APL]], sharing its [[glyph]] with [[Commute]], and was adopted in [[Dyalog APL 18.0]] as an alternative to the constant [[dfn]] such as <source lang=apl inline>{0}</syntaxhighlight>. | ||
== Examples == | == Examples == | ||
The need for Constant arises in various contexts, such as at the rightmost branch in a [[train]] and mapping over an array to create a constant-filled one. The major advantage of Constant <source lang=apl inline>A⍨</ | The need for Constant arises in various contexts, such as at the rightmost branch in a [[train]] and mapping over an array to create a constant-filled one. The major advantage of Constant <source lang=apl inline>A⍨</syntaxhighlight> over a constant dfn <source lang=apl inline>{A}</syntaxhighlight> is that the array <source lang=apl inline>A</syntaxhighlight> is evaluated only once at definition time, rather than every time the function is called. | ||
=== Trains === | === Trains === | ||
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f5←+*3⍨ ⍝ A solution using Constant | f5←+*3⍨ ⍝ A solution using Constant | ||
</ | </syntaxhighlight>{{Works in|[[Extended Dyalog APL]], [[Dyalog APL 18.0]]}} | ||
=== Other uses === | === Other uses === | ||
Sometimes, one needs a constant function that returns one of the arguments of the outer dfn. Simply writing <source lang=apl inline>{⍺}</ | Sometimes, one needs a constant function that returns one of the arguments of the outer dfn. Simply writing <source lang=apl inline>{⍺}</syntaxhighlight> does not work; <source lang=apl inline>⍺⍨</syntaxhighlight> does. | ||
<source lang=apl> | <source lang=apl> | ||
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1 0 0 1{'⎕'@(⍺⍨)⍵}'AbcD' | 1 0 0 1{'⎕'@(⍺⍨)⍵}'AbcD' | ||
⎕bc⎕ | ⎕bc⎕ | ||
</ | </syntaxhighlight>{{Works in|[[Extended Dyalog APL]], [[Dyalog APL 18.0]]}} | ||
Using Constant is also cleaner when doing a constant fill. | Using Constant is also cleaner when doing a constant fill. | ||
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1 1 1 | 1 1 1 | ||
1 1 1 | 1 1 1 | ||
</ | </syntaxhighlight>{{Works in|[[Extended Dyalog APL]], [[Dyalog APL 18.0]]}} | ||
== External links == | == External links == | ||