Fold (higher-order function): Difference between revisions

Revision as of 11:02, 30 September 2024

Revision as of 17:28, 5 December 2024

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

|

| 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 |url= http://permalink.gmane.org/gmane.comp.lang.scala/9557 |access-date= 14 October 2013 |archive-url= https://web.archive.org/web/20150514122827/http://permalink.gmane.org/gmane.comp.lang.scala/9557 |archive-date= 14 May 2015}}</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’sScala's /: operator (foldLeft)|date=28 July 2010 |url=https://nicholassterling.wordpress.com/2010/07/28/an-intuition-about-scalas-operator-foldleft/|access-date=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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|title= A tutorial on the universality and expressiveness of fold

|journal= Journal of Functional Programming

|issuedate= 9 (4)1999

|volume= 9

|issue= 4

|pages= 355–372

|doi= 10.1017/S0956796899003500

|url= http://www.cs.nott.ac.uk/~gmh/fold.pdf

|access-date= March 26, 2009}}</ref>