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Discussion on: Purely Functional Python With Static Types

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Sune Debel Author • Edited

I think there are pros and cons to both solutions. The reason I chose to bake error handling into our IO type here is because the python type system doesn't support higher-kinded types, and in general, in order to compose effects "horizontally" as you suggest with type safety (e.g with monad transformers) you need higher-kinded types. For that reason I think this "vertical" effect composition is more well suited for Python.

I'm not sure I understand your question completely, but I take it to be: How does error handling work when you compose Effect and list (i.e Effect[List[int]]). My library doesn't provide any special helper methods for that case (I'm not sure why you would need it), but if you swap the order of composition to List[Effect[int]], you can use many different provided helper functions to produce new effects that aggregate on such a list, e.g sequence_async(List[Effect[int]]) -> Effect[List[int]] (semantically equivalent to sequence in haskell). In that case if one effect in the list fails, the resulting effect also fails (again, same as in haskell). Apologies if I misunderstood your comment :)