You invoke an intrinsic by calling it explicitly from within a
program, subprogram, or procedure. All system intrinsics are treated
as external procedures by user programs and the intrinsics mechanism
facilitates the declaration.
To call an intrinsic, you must know the following information:
The number of parameters and whether any are optional
The data type of each parameter and whether parameters are passed
by value or reference
The calling sequence or order of the parameters
The functional return value, if applicable
