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Check

Check

Check[expr,failexpr]

evaluates expr, and returns the result, unless messages were generated, in which case it evaluates and returns failexpr.

Check[expr,failexpr,{s₁::t₁,s₂::t₂,…}]

checks only for the specified messages.

Check[expr,failexpr,"name"]

checks only for messages in the named message group.

Details

Check has attribute HoldAll.
Check does not test for messages that have been switched off using Off, or by uses of Quiet that occur inside it.
The operation of Check is not affected by being enclosed inside Quiet.
In Check[expr,failexpr,"name"], possible named message groups are given by $MessageGroups.
Explicit message names of the form s::t can be mixed with named message groups.

Examples

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Basic Examples (2)

Return err when any message is issued:

Check only for specific messages:

Scope (3)

Check for a message from a specific function:

The ArcTan::indet is not caught by Check:

Use the head General to catch the message from any function:

Catch multiple messages:

Check for a message from a named group:

Applications (1)

Use Check and Quiet to provide values for arguments where a function is not applicable:

This function simply returns its argument if its argument is a string of length less than four:

Without the Check and Quiet, the middle input would have returned unevaluated with a message:

Properties & Relations (3)

Check does not prevent messages from being issued:

Check does not detect messages suppressed with a inner Quiet:

However, the operation of Check is not affected by being inside Quiet:

Check does not report messages that have been turned off:

Restore the message:

Possible Issues (1)

A nested Check does not silence a message for an enclosing Check:

Use an intermediate Quiet to prevent the enclosing Check from reacting to the message:

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