[tel]

In Haskell, that's usually that's done using `do` syntax.

    do
      a <- somePartialResult
      b <- partialFunction1 a
      c <- partialFunction2 a b
      return c

where we assume signatures like

    somePartialResult : Either<A, Error>
    partialFunction1 : A -> Either<B, Error>
    partialFunction2 : A -> B -> Either<C, Error>

this overall computation has a signature Either<C, Error>. The way it works is that the first failing computation (the first Either that's actually Left-y) will short-circuit and become the final result value. Only if all of the partial computations succeed (are Right-y) will the final result by Right(c).

In Haskell we don't have an early return syntax like `return` and function scope. Instead, we construct something equivalent using `do` syntax. This can be a little weightier than `return`, but the upside is that you can construct other variants of things like early returns that can be more flexible.

[me_vinayakakv]

Nice! Would it be possible to transform an error to something else using this syntax?

Or, should we resort to a method of `Either` that transforms its `Left` in that case?

[tel]

Unfortunately, no. Or, rather, I'm sure there's a way to make it happen although that's not typical practice. Typically you'd resort to mapping the left sides of your eithers so that the error types match.

Rust offers a similar facility (though specialized to just handle a couple kinds of error handling) using its `?` syntax. This works essentially identically to the do syntax above, but also includes a call to transform whatever error type is provided into the error type of the function return.

Note that in Rust (a) this technique only, today, works at function boundaries and (b) will always be explicitly annotated since all functions require an explicit type. This helps a bit over Haskell's more general approach as it provides some additional data to help type inference along.

That said, if you were interested, it's likely possible to emulate something very similar to Rust's technique in Haskell, too.

But I don't think I've ever seen that. It just doesn't feel as stylish in Haskell. The From/Into traits define a behavior that's much more pervasive than most type classes in Haskell. It works well for Rust, but is I think less compelling to the Haskell community.