[Python-ideas] "Sum" Type hinting [was: Type hinting for path-related functions]
k7hoven at gmail.com
Mon May 16 10:45:41 EDT 2016
On Mon, May 16, 2016 at 4:57 AM, Guido van Rossum <guido at python.org> wrote:
> unions in Python are always tagged (since you can always introspect the object type).
I suppose that is true at runtime, at least if the pairwise
intersections of the "arguments" of the union are empty as they
usually are. But for a static type checker, the "tag" for the Union
may be missing (which is the thing I was worried about).
> in Haskell as in PEP 484, Sum types and generics are pretty much orthogonal
Although the parametrization provided by generics make TypeVars more
powerful for annotating functions that deal with the equivalent of sum
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