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OptionalElement[patt]

is a grammar rules pattern object that represents 0 or 1 instances of patt.

OptionalElement[patt,default]

uses default if the element is not present.

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OptionalElement

OptionalElement[patt]

is a grammar rules pattern object that represents 0 or 1 instances of patt.

OptionalElement[patt,default]

uses default if the element is not present.

Details

Examples

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Basic Examples  (2)

Allow certain words to be optional:

Wolfram Language code: grammar = CloudDeploy[ GrammarRules[{FixedOrder[OptionalElement["from"], from : GrammarToken["City"], "to", to : GrammarToken["Ocean"]] :> from -> to}] ]
Wolfram Language code: GrammarApply[grammar, "Boston to the Pacific"]

Supply a default value for a missing element:

Wolfram Language code: grammar = CloudDeploy[ GrammarRules[{FixedOrder[OptionalElement["from"], from : OptionalElement[GrammarToken["City"], None], "to", to : GrammarToken["Ocean"]] :> Replace[from, None -> $GeoLocationCity] -> to}] ]
Wolfram Language code: GrammarApply[grammar, "Boston to the Pacific"]
Wolfram Language code: GrammarApply[grammar, "to the Pacific"]

Possible Issues  (1)

The default value evaluates immediately:

Wolfram Language code: CloudGet[CloudDeploy[ GrammarRules[{FixedOrder[OptionalElement["from"], from : OptionalElement[GrammarToken["City"], $GeoLocationCity], "to", to : GrammarToken["Ocean"]] :> from -> to}] ]]

Use a sentinel for a dynamic default value:

Wolfram Language code: grammar = CloudDeploy[ GrammarRules[{FixedOrder[OptionalElement["from"], from : OptionalElement[GrammarToken["City"], None], "to", to : GrammarToken["Ocean"]] :> Replace[from, None -> $GeoLocationCity] -> to}] ]
Wolfram Language code: GrammarApply[grammar, "to the Pacific"]
Wolfram Research (2015), OptionalElement, Wolfram Language function, https://reference.wolfram.com/language/ref/OptionalElement.html.

Text

Wolfram Research (2015), OptionalElement, Wolfram Language function, https://reference.wolfram.com/language/ref/OptionalElement.html.

CMS

Wolfram Language. 2015. "OptionalElement." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/OptionalElement.html.

APA

Wolfram Language. (2015). OptionalElement. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/OptionalElement.html

BibTeX

@misc{reference.wolfram_2026_optionalelement, author="Wolfram Research", title="{OptionalElement}", year="2015", howpublished="\url{https://reference.wolfram.com/language/ref/OptionalElement.html}", note=[Accessed: 13-June-2026]}

BibLaTeX

@online{reference.wolfram_2026_optionalelement, organization={Wolfram Research}, title={OptionalElement}, year={2015}, url={https://reference.wolfram.com/language/ref/OptionalElement.html}, note=[Accessed: 13-June-2026]}