From Modelica 2.x:
Returns true if the formal input or output argument ident
is present as an actual argument of the function call. If the argument is not
present, isPresent(ident) may return false [but may also return true e.g. for
implementations that always compute all results]. isPresent() should be used for
optimisation only and should not influence the results of outputs that are present
in the output list. It can only be used in functions.
OpenModelica returns false for other output formal parameters that are not present in the function call (except the first output, which is always considered present).
OpenModelica gives a compile-time error if the variable is not an input or output formal parameter.
function isPresent<T> input T ident; output Boolean b; end isPresent;