Details

This message is generated when a pattern based on Optional is used without specifying a default value for the pattern.
The notation patt. is used for Optional[patt].
Assignments to Default are used for specifying default values for Optional patterns.
Off[message] switches off the message; On[message] switches it on. For example: Off[Pattern::nodef].

Examples

A Default value has not been assigned for an Optional pattern in the test function:

Wolfram Language code: test[] /. test[p_.] -> {p, p + 1}

This shows a valid assignment to Default for use with an Optional pattern that occurs as an argument in the test function:

Wolfram Language code: Default[test, 1] = 0

Wolfram Language code: test[] /. test[p_.] -> {p, p + 1}

Clear the Default rule for the test function:

Wolfram Language code: Default[test, 1]=.

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