> semantically, `Either<Nothing, Either<T...

# arrow

[pakoito]

semantically, Either<Nothing, Either<Throwable, Int>> is correct

so you fold({ exception }, { it.fold({ error }, { success })})

[Gopal S Akshintala]

Hi @pakoito, if this is semantically right, where is E in IO<E,A> used? I am confused between the use-case difference btw using Either for A, compared to IO<E,A>

[pakoito]

It’s Nothing

[pakoito]

in your case

[pakoito]

IO<A> has A or Exception. IO<E, A> has A, exception, or error

[pakoito]

when you attempt, you put the exception into an Either as the A

[Gopal S Akshintala]

Error as in non-recoverable?

[pakoito]

error as in domain error

[pakoito]

exception as in unexpected

[Gopal S Akshintala]

Ok, got it! in that case, how can I raise a domain error within the IO {} block?

[pakoito]

IO.raiseError

[pakoito]

oh

[pakoito]

within the block

[Gopal S Akshintala]

yes

[pakoito]

I see what API you’re missing

[pakoito]

gimme asec, lemme find it

[Gopal S Akshintala]

sure

[Gopal S Akshintala]

thanks

[pakoito]

there’s none, I’ll fill a ticket for it

[Gopal S Akshintala]

awesome! thanks

[pakoito]

https://github.com/arrow-kt/arrow-fx/issues/145

[Gopal S Akshintala]

Cool!