🚀 go-pugleaf

So far, people have given lots of examples of lists of union types.
Message queues, for instance, are usually union types. The arguments to
printf are union types (though they're not typechecked---I think most
people consider this a flaw in the interface). Symbolic manipulation
routines deal with union types.

People have also given the example of ``list of object that understands
foo,'' where foo is an operation. In object-oriented languages, such
objects are basic types anyway, so these *still* aren't heterogeneous
lists.

Does anyone have an example of a heterogeneous list---something beyond
unions and callback functions---used in a real program?

I suspect not. After all, if a module is like printf and understands
all the possible types of objects in the list, it's dealing with a union
type. If a module does not know all the possible types, it's going to
see just a set of function pointers, and it won't even *want* to deal
with the object except through those function pointers. If there is a
middle case, how would you use it?

---Dan