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Mathematica > Core Language > Tuning & Debugging > Symbol Handling >

Mathematica > Core Language > Package Development > Namespace Management > Symbol Handling >

Built-in Mathematica Symbol

ValueQ

ValueQ[expr]
gives True if a value has been defined for expr, and gives False otherwise.

ValueQ gives False only if expr would not change if it were to be entered as Mathematica input.

Only the one argument form of

has values associated with it:

Only the one argument form of

has values associated with it:

Values of symbols:

Function definitions:

Conditional definitions; the result depends on the argument:

Here x is evaluated before ValueQ sees it:

Use Unevaluated to preserve the HoldAll attribute:

Pi evaluates to itself:

Use NumericQ to find out whether there is a numerical value defined:

ValueQ returns True if any evaluation takes place, even though

does not match here: