> If you just want to signalize a fail case without any additional
> information, then a Maybe fits better than an Either, because
> why should you need this bogus empty string?

Now it looks to me that it might be better and more consistent to write an empty bogus string (as with: nothing = Left "") than to have two distinct ways of error reporting, and both are used widely and often should be intermixed.
And at the end, call site could decide does it want to use the string or not.