Check¶

Returns its first argument unless a message is emitted, in which case it returns the second argument.

$ wo 'Check[1/2, error]'
1/2

A message counts as soon as it is generated. General::stop keeps the fourth and later ones from being printed, but Check still reacts to them — here the outer Quiet keeps the three printed ones out of the way:

$ wo 'Quiet[Table[Check[1/0, "F"], {6}]]'
{F, F, F, F, F, F}

A Quiet inside the Check does stop it; one outside does not:

$ wo 'Check[Quiet[1/0], "F"]'
ComplexInfinity

$ wo 'Quiet[Check[1/0, "F"]]'
F

Check reacts to messages, not to control flow, so a Throw passes straight through it:

$ wo 'Catch[Check[Throw[1], "F"]]'
1