On
Details
- Some messages for built-in functions are off by default, and must explicitly be switched on using On .
- In On ["name"], possible named message groups include:
-
"Compiler" warnings associated with compiled code"Graphics" warnings associated with graphics generation"Packing" notifications associated with packed arrays"Spelling" spell-checking messages for symbol names"Symbolics" warnings associated with symbolic computation
- $MessageGroups gives a complete list of message groups recognized by On .
- On [General::name] switches on all messages derived from General::name.
- When tracing is switched on, each evaluation of a symbol, on its own or as a function, is printed, together with the result.
- Note that the tracing information is printed when a function returns. As a result, traces of recursive functions appear in the opposite order from their calls.
- On [Assert ] switches on messages associated with assertions specified by Assert .
- On [s] is equivalent to On [s::trace].
Examples
open all close allBasic Examples (2)
Turn on a message that is issued whenever a new symbol is created:
Now when a new symbol is created the message is issued:
This turns the message back off:
Messages about unpacking are off by default:
Turn them on:
Restore the default behavior:
Scope (2)
Operations on symbols normally are done silently:
Use On to enable tracing of the symbol:
Restore the default behavior:
Turn on multiple messages:
Restore the default behavior:
See Also
Tech Notes
Related Guides
Related Workflows
- Understand Error Messages
History
Introduced in 1988 (1.0) | Updated in 2008 (7.0) ▪ 2010 (8.0)
Text
Wolfram Research (1988), On, Wolfram Language function, https://reference.wolfram.com/language/ref/On.html (updated 2010).
CMS
Wolfram Language. 1988. "On." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2010. https://reference.wolfram.com/language/ref/On.html.
APA
Wolfram Language. (1988). On. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/On.html
BibTeX
@misc{reference.wolfram_2025_on, author="Wolfram Research", title="{On}", year="2010", howpublished="\url{https://reference.wolfram.com/language/ref/On.html}", note=[Accessed: 05-December-2025]}
BibLaTeX
@online{reference.wolfram_2025_on, organization={Wolfram Research}, title={On}, year={2010}, url={https://reference.wolfram.com/language/ref/On.html}, note=[Accessed: 05-December-2025]}