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{{Built-in|Power|⍣}} is a primitive [[dyadic operator]] that performs bounded looping, unbounded looping, and function | {{Built-in|Power|⍣}} is a primitive [[dyadic operator]] that performs bounded looping, unbounded looping, and function [[inverse]]s in [[NARS2000]], [[Dyalog APL]], and related implementations like [[ngn/apl]], [[dzaima/APL]], and [[Extended Dyalog APL]]. | ||
== Description == | == Description == | ||
A call to Power is of the form <source lang=apl inline>X(f⍣g)Y</source>, where | A call to Power is of the form <source lang=apl inline>X(f⍣g)Y</source>, where | ||
* <source lang=apl inline>X</source> is an optional argument. | * <source lang=apl inline>X</source> is an optional argument. | ||
* <source lang=apl inline>f</source> is a function. If <source lang=apl inline>X</source> is given, it is bound to <source lang=apl inline>f</source> | * <source lang=apl inline>f</source> is a function. If <source lang=apl inline>X</source> is given, then it is bound to <source lang=apl inline>f</source> so <source lang=apl inline>X f⍣g Y</source> is equivalent to <source lang=apl inline>X∘f⍣g Y</source>. | ||
* <source lang=apl inline>g</source> can be an | * <source lang=apl inline>g</source> can be an [[array]] or a function. | ||
Power repeatedly applies <source lang=apl inline>f</source> to <source lang=apl inline>Y</source> based on the type of operand <source lang=apl inline>g</source>: | Power repeatedly applies <source lang=apl inline>f</source> to <source lang=apl inline>Y</source> based on the type of operand <source lang=apl inline>g</source>: | ||
* '''Function''': Must be dyadic and must return a boolean | * '''Function''': Must be dyadic and must return a boolean [[singleton]]. The previous iteration value is provided as left argument to <source lang=apl inline>f</source>, and the current iteration value is given as right argument. <source lang=apl inline>f</source> is repeatedly applied until this function returns 1. | ||
* '''Integer''': | * '''Integer''': Applies <source lang=apl inline>f</source> <source lang=apl inline>g</source> times to <source lang=apl inline>Y</source>. If <source lang=apl inline>g</source> is negative, then the inverse of <source lang=apl inline>f</source> (if available) is applied. | ||
* '''Integer Array''': In [[Extended Dyalog APL]], <source lang=apl inline>g</source> can be an integer array. Each integer <source lang=apl inline> | * '''Integer Array''': In [[Extended Dyalog APL]], <source lang=apl inline>g</source> can be an integer array. Each integer <source lang=apl inline>i</source> in <source lang=apl inline>g</source> will be replaced by <source lang=apl inline>⊂(f⍣i)Y</source>. | ||
== Examples == | == Examples == | ||
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* [https://help.dyalog.com/latest/#Language/Primitive%20Operators/Power%20Operator.htm Dyalog] | * [https://help.dyalog.com/latest/#Language/Primitive%20Operators/Power%20Operator.htm Dyalog] | ||
* J [https://www.jsoftware.com/help/dictionary/d202n.htm Dictionary], [https://code.jsoftware.com/wiki/Vocabulary/hatco NuVoc] | * J [https://www.jsoftware.com/help/dictionary/d202n.htm Dictionary], [https://code.jsoftware.com/wiki/Vocabulary/hatco NuVoc] | ||
{{APL built-ins}}[[Category:Primitive operators]] | |||