Re:An epic treatise on error models for systems programming ...
by marcosdumay on Saturday March 08, 2025 @01:10PM
(#43302109)
Yes, unions are the proper type sums. Just as fixed cardinality sets are the proper type products, not tuples. I didn't know about this feature in Scala 3, all it seems to be missing for a fully algebraic sum is type negation (like `FileError and not FileSeekUnsupportedError`).
> At the same time Maybe<Maybe<String>> may encode a useful state that will be unrepresentable with `(String | None) | None = String | None`.
We already have the operation that takes a type and converts it into a non-matching type. It doesn't have a well accepted name, in Haskell it's called `newtype` but every language with strict types has it.
There is no need to mix those operations in the fundamental types in a language. The usual emuns and tuples are just less expressive suggared synonyms.
> At the same time Maybe<Maybe<String>> may encode a useful state that will be unrepresentable with `(String | None) | None = String | None`.
We already have the operation that takes a type and converts it into a non-matching type. It doesn't have a well accepted name, in Haskell it's called `newtype` but every language with strict types has it.
There is no need to mix those operations in the fundamental types in a language. The usual emuns and tuples are just less expressive suggared synonyms.