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Comment by greener_grass | Hacker News Reader

Here `a` and `b` can have different types:

    let! a = fetchA() and! b = fetchB()

Whereas `Promise.all` usually requires all promises to have the same type (returning a `List<T>` or even a `List<obj>`) .

Actually, TypeScript's `Promise.all` can handle different types too.

    const [a, b] = await Promise.all([fetchA(), fetchB()]); // => a: A, b: B

I am talking about C# / F# context where the lists must have homogeneous types.

That TypeScript supports this is yet more complexity introduced to cover usages of an API not designed around types.