Fold (higher-order function): Difference between revisions

Revision as of 07:59, 6 November 2020

Revision as of 17:50, 29 November 2020

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| <code>''list''.reduceRight(''func'')</code>

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| Scala's symbolic fold syntax was intended to resemble the left- or right-leaning tree commonly used to explain the fold operation,<ref>{{cite newsgroup |title= Re: Blog: My verdict on the Scala language |author= Odersky, Martin |date= 2008-01-05 |newsgroup= comp.scala.lang |message-id= |url= http://permalink.gmane.org/gmane.comp.lang.scala/9557 |accessdate= 14 October 2013}}</ref> but has since been reinterpreted as an illustration of a toppling domino.<ref>{{cite web|last1=Sterling|first1=Nicholas|title=An intuitive feel for Scala’s /: operator (foldLeft)|url=https://nicholassterling.wordpress.com/2010/07/28/an-intuition-about-scalas-operator-foldleft/|accessdate=24 June 2016}}</ref> The colon comes from a general Scala syntax mechanism whereby the apparent infix operator is invoked as a method on the left operand with the right operand passed as an argument, or vice versa if the operator's last character is a colon, here applied symmetrically.

Scala also features the tree-like folds using the method <code>list.fold(z)(op)</code>.<ref>{{Cite web|url=https://www.scala-lang.org/api/current/scala/collection/Seq.html#fold%5BA1%3E:A%5D(z:A1)(op:(A1,A1)=%3EA1):A1|title=Fold API - Scala Standard Library|website=www.scala-lang.org|access-date=2018-04-10}}</ref>

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