Open Radar

 
Summary:
Enumerations’ cases can specify the structure of data (the fields of the tuple they’re associated with, if any) and functionality (the cases interior to switch/case statements in functions taking the enumeration); i.e. they define limitations on what can be an element of that case and provide a hook for behaviour. This is pretty much what types are.

But since they’re not types, just tagged unions, they’re a weaker, runtime standin for an actual type and you can‘t do pattern matching against them in the type system, only in switch/case. Likewise, you can’t do type checking in switch/case, only in the type system; they ought to be one and the same.

If they were, I would be able to define my program parametrically bringing the full force of the language to bear on things like unwrapping cyclic graphs. Since they’re not, I have a small number of much less convenient options available to me, which typically run into other problems (like the lack of type-parameterized protocols).


Steps to Reproduce:
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Expected Results:
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Actual Results:
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Regression:
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Notes:
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