Intercepting the Creation of New Symbols

Mathematica creates a new symbol when you first enter a particular name. Sometimes it is useful to "intercept" the process of creating a new symbol. Mathematica provides several ways to do this.

On[General::newsym]print a message whenever a new symbol is created
Off[General::newsym]switch off the message printed when new symbols are created

Printing a message when new symbols are created.

This tells Mathematica to print a message whenever a new symbol is created.
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Mathematica now prints a message about each new symbol that it creates.
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This switches off the message.
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Generating a message when Mathematica creates a new symbol is often a good way to catch typing mistakes. Mathematica itself cannot tell the difference between an intentionally new name, and a misspelling of a name it already knows. But by reporting all new names it encounters, Mathematica allows you to see whether any of them are mistakes.

$NewSymbola function to be applied to the name and context of new symbols which are created

Performing operations when new symbols are created.

When Mathematica creates a new symbol, you may want it not just to print a message, but instead to perform some other action. Any function you specify as the value of the global variable $NewSymbol will automatically be applied to strings giving the name and context of each new symbol that Mathematica creates.

This defines a function to be applied to each new symbol which is created.
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The function is applied once to and once to .
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