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Throw[value]

stops evaluation and returns value as the value of the nearest enclosing Catch.

Throw[value,tag]

is caught only by Catch[expr,form], where tag matches form.

Throw[value,tag,f]

returns f[value,tag] as the top-level value if no appropriate Catch is found.

Details
Details and Options Details and Options
Examples  
Basic Examples  
Scope  
Generalizations & Extensions  
Applications  
Properties & Relations  
Possible Issues  
See Also
Tech Notes
Related Guides
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Throw

Throw[value]

stops evaluation and returns value as the value of the nearest enclosing Catch.

Throw[value,tag]

is caught only by Catch[expr,form], where tag matches form.

Throw[value,tag,f]

returns f[value,tag] as the top-level value if no appropriate Catch is found.

Details

  • You can use Throw and Catch to exit functions such as Nest, Fold, FixedPoint, and Scan.
  • tag can be any expression.
  • tag in Throw[value,tag] is reevaluated every time it is compared to form in Catch[expr,form].
  • An error is generated and an unevaluated Throw is returned if there is no appropriate enclosing Catch to catch the Throw.

Examples

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Basic Examples  (3)

Exit to the enclosing Catch as soon as Throw is evaluated:

Define a function that can "throw an exception":

The result of Catch is just what is thrown by Throw:

Use Throw to exit a loop when a criterion is satisfied:

Scope  (4)

Throw works inside essentially any function:

Use Throw to throw any type of expression:

Throw is caught by the nearest enclosing Catch:

As soon as the first Throw is evaluated, it exits to the enclosing Catch:

Generalizations & Extensions  (3)

Catch Throw with tag u:

The inner Catch catches Throw:

The outer Catch catches Throw:

Keep the tag local:

Applications  (3)

Find the next prime after 1010:

Find the first power of 17 equal to 1 mod 19:

Stop if an iteration gets too large:

Properties & Relations  (1)

Use Check to throw an exception if a message is generated:

Possible Issues  (2)

Throw requires Catch:

Using Throw can affect the structure of what is returned by a function:

Wolfram Research (1988), Throw, Wolfram Language function, https://reference.wolfram.com/language/ref/Throw.html (updated 2020).

Text

Wolfram Research (1988), Throw, Wolfram Language function, https://reference.wolfram.com/language/ref/Throw.html (updated 2020).

CMS

Wolfram Language. 1988. "Throw." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2020. https://reference.wolfram.com/language/ref/Throw.html.

APA

Wolfram Language. (1988). Throw. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/Throw.html

BibTeX

@misc{reference.wolfram_2025_throw, author="Wolfram Research", title="{Throw}", year="2020", howpublished="\url{https://reference.wolfram.com/language/ref/Throw.html}", note=[Accessed: 13-August-2025]}

BibLaTeX

@online{reference.wolfram_2025_throw, organization={Wolfram Research}, title={Throw}, year={2020}, url={https://reference.wolfram.com/language/ref/Throw.html}, note=[Accessed: 13-August-2025]}