Problem with function return

["Amgarp" <PhyrePhox@firemail.de>]

Hi,

please help me with the following Problem:

Main programm:

type color is (red,gree,blue);

col:color;

col:=some_function(parameter);

Now, "some_function" returns of course a color type,
but when the parameter is bad(e.g. an empty string), an exception will be
raised.

What should the function return then?

Without a return statement in the e-handler there'll be a
Programm_Error.

Is there a way to prevent the line "col:=some_function(parameter);"
to be evaluated, or should it just return "some"(but of course wrong)
value?

Thanks!