Tagged union

[cdonovick]

Adds TaggedUnion syntax as described in cdonovick/peak#68 (comment)

Breaks GarnettFlow because change to internal interfaces that magma will have to adopt but it should be a 1 line change in magma/product.py

[rdaly525]

Tests look good.

If I understand correctly, each ADT type is either "attribute based" and/or "getitem based". Each ADT metaclass can now inherit from one or both of these and have the fields accessed via attribute and/or getitem. In addition one can specify if each of these ADT types are ordered. This would probably make it easier to make a coproduct adt type (ordered Sum) or an unordered Product.

[rdaly525]

One minor issue, is that I am sure we have code scattered throughout that checks if a type is (Product, Tuple, Sum). These will have to be augmented to included tagged union. This should not block the PR though.

[cdonovick]

@rdaly525

If I understand correctly, each ADT type is either "attribute based" and/or "getitem based". Each ADT metaclass can now inherit from one or both of these

Correct

and have the fields accessed via attribute and/or getitem

In practice yes but not really what's going on. AttrSyntax defines fields with attributes (x = int), it does not however mandate anything about the generated class. It just collects the fields and hands them off to _from_fields. GetitemSyntax defines fields with __getitem__ and again doesn't mandate anything about how the index should be interpreted. For instance AbstractBitvectorMeta could be potentially inherit from GetitemSyntax.

In addition one can specify if each of these ADT types are ordered. This would probably make it easier to make a coproduct adt type (ordered Sum) or an unordered Product

Correct
.

[phanrahan]

Looks good to me! Tests are clear.