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Pattern::nodef

Pattern::nodef

更多信息

  • 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].

范例

基本范例  (1)

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

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

Clear the Default rule for the test function: