How can I create a type which will be choice of other types?

Hi,

I want to create a simpleType which would be a choice between other 
types(some of them are build-in and some constructed by me). I have tried 
to do it but it did not work. The problem is that I cannot use the choice 
for different types.Has anybody any idea how can I create this type??

Thanks in advance
Marios


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