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Scalar extension: Difference between revisions
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=== Singleton extension === | === Singleton extension === | ||
Most APLs treat arrays with one element ([[singleton]]s) as scalars for the purposes of scalar extension. While often referred to simply as "scalar extension", this practice could more precisely be called "singleton extension". For example, | |||
<syntaxhighlight lang=apl> | <syntaxhighlight lang=apl> | ||
(1 1⍴5) + 10 20 | (1 1⍴5) + 10 20 | ||
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2 | 2 | ||
</syntaxhighlight> | </syntaxhighlight> | ||
In this case addition accepts a singleton, and discards its shape. If two singletons are used as arguments, they are still considered to [[Conformability|conform]]; the shape of the result is taken from the argument with higher rank. | In this case addition accepts a singleton, and discards its shape. If two singletons are used as arguments, they are still considered to [[Conformability|conform]]; the shape of the result is taken from the argument with higher rank. | ||
Singleton extension was supported in [[APL\360]] by 1970<ref>S. Charmonman. [https://dl.acm.org/doi/10.1145/987461.987468 A generalization of APL array-oriented concept]. [[APL Quote Quad]] Volume 2, Number 3. 1970-09.</ref> and is generally present in later APLs. However, [[APL2]] and specification [[ISO/IEC_13751:2001]] only extend a one-element vector and not any singleton,<ref>[[Roger Hui]] and [[Morten Kromberg]]. [https://dl.acm.org/doi/abs/10.1145/3386319 ''APL since 1978'']. ACM HOPL IV. 2020-06. §2.1 Tally.</ref> and some newer dialects such as [[dzaima/APL]] and [[Kap]] don't implement singleton extension. | |||
Singleton extension can sometimes conflict with other extensions, an issue which does not occur with scalar extension. If a function is extended to allow a shorter vector argument to be extended (perhaps by padding with 0), but it also supports singleton extension, then there is a conflict with length-1 vectors. | Singleton extension can sometimes conflict with other extensions, an issue which does not occur with scalar extension. If a function is extended to allow a shorter vector argument to be extended (perhaps by padding with 0), but it also supports singleton extension, then there is a conflict with length-1 vectors. | ||
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== References == | |||
<references/> | |||
{{APL features}}[[Category:Function characteristics]][[Category:Conformability]] | {{APL features}}[[Category:Function characteristics]][[Category:Conformability]] | ||