6.12.6.5. Discriminated union

We implement a discriminated union by tagging the argument categories with unique tags, and forming the undiscriminated union. It would be better to use the actual categories as their own tags but that would not work if the same category was presented twice in the argument list, which is likely to be the most common case.
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   130: #line 160 "felix_cons.ipk"
   131: def cat_dunion(*args):
   132:   cats = []
   133:   for cat in args:
   134:     cats.append(cat_tagged(unique_tag(),cat))
   135:   return apply(cat_union, tuple(cats))
   136: 
    10: #line 26 "felix_package.ipk"
    11: