> The `Either a b` type in Haskell is equivalent to the `Result<T, Error>` type in other languages. The only difference is in the naming:

This is false and misleading.

The Result <E, T> usually (C#, at the very least, most probably C++ and many other languages) should always be fully instantiated. One usually cannot construct a type "function" like Result <E,> that needs a single type argument to instantiate a full type. The partial application on type level is not there in most languages, including Rust (a result of a little googling).

The Haskell's Either type can be instantiated to Be a two-type-arguments function, one type argument function and, finally, a fully instantiated type like Either String Int.

This means that Result <E, T> type effectively has a single type argument, namely pair of types. The Either type has two type arguments and can be partially applied.