When you call a procedure or function, program control passes from the point where the call is made to the body of the routine. You can make the call using the routine's declared name (with or without qualifiers) or using a procedural variable that points to the routine. In either case, if the routine is declared with parameters, your call to it must pass parameters that correspond in order and type to the routine's parameter list. The parameters you pass to a routine are called actual parameters, while the parameters in the routine's declaration are called formal parameters.

When calling a routine, remember that

• expressions used to pass typed const and value parameters must be assignment-compatible with the corresponding formal parameters.
• expressions used to pass var and out parameters must be identically typed with the corresponding formal parameters, unless the formal parameters are untyped.
• only assignable expressions can be used to pass var and out parameters.
• if a routine's formal parameters are untyped, numerals and true constants with numeric values cannot be used as actual parameters.

When you call a routine that uses default parameter values, all actual parameters following the first accepted default must also use the default values; calls of the form SomeFunction(,,X) are not legal.
You can omit parentheses when passing all and only the default parameters to a routine. For example, given the procedure

procedure DoSomething(X: Real = 1.0; I: Integer = 0; S: string = '');

the following calls are equivalent.

DoSomething();
DoSomething;