# Mathematica: How mimic pattern matching of arguments for Boolean?

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Surprisingly there is no "Boolean" in the Wolfram Language, and True and False are just Symbols:
``````
o: Symbol

o: Symbol

i: testBool = True
o: Symbol
``````
So pattern matching in function arguments does not behave as one might expect:
``````
i: fNoMatchToBool[arg_Boolean:True] := "Will not actually match True or False";

i: fNoMatchToBool[testBool] (* Not seen, does not match, will just bounce *)
o: fNoMatchToBool[True]
``````
Also, because of the defined argument default, this does work:
``````
I: fNoMatchToBool[]
o: Will not actually match True or False
``````
But you can HACK a match by using an argument value set test:
``````
i: fHackMatchBool[arg:True|False] := "Will match True or False"';
i: fFakeMatchBool[testBool]
o: "Will match True or False"
``````

Note, however, that if use this trick you can't then specify a Boolean default for the argument.

The most MMA-keen of MMA fans might claim that's not a hack, but certainly the lack of "Boolean" argument matching is a "gotcha". Note that BooleanQ gives True on either True or False, making it slightly more surprising that there isn't comparable argument pattern matching.

``````
I: BooleanQ[testBool]
o: True
``````
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