You use function calls to call routines in registered function libraries. Evaluate does not perform any function parameter checks at parse time and it does not check that the function exists in any of the registered function libraries. Function checks and parameter type checks are only performed when the expression is executed. This ensures that the appropriate type checks are performed when an expression program is run on a computer that has different function libraries registered.

Some functions in the Function Library need to be told to which variable the function applies. This enables the function to access the variable's metadata, its current value, or both. These functions can be called in two ways: by passing the name of the variable as an explicit parameter, or by preceding the function call with the variable's name and omitting the variable parameter. For example, the following two calls are equivalent: