[Haskell-cafe] Why Maybe exists if there is Either?

[Niklas Larsson]

Maybe doesn't have to be used for error reporting. Optional values is a very big use case for it.

----- Ursprungligt meddelande -----
Från: "Vlatko Basic" <vlatko.basic at gmail.com>
Skickat: ‎2014-‎01-‎09 16:37
Till: "haskell-cafe at haskell.org" <haskell-cafe at haskell.org>
Ämne: Re: [Haskell-cafe] Why Maybe exists if there is Either?

Hi Daniel,

 > 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.


vlatko


-------- Original Message  --------
Subject: Re: [Haskell-cafe] Why Maybe exists if there is Either?
From: Daniel Trstenjak <daniel.trstenjak at gmail.com>
To: haskell-cafe at haskell.org
Date: 09.01.2014 16:13

>
> Hi Vlatko,
>
> On Thu, Jan 09, 2014 at 03:50:16PM +0100, Vlatko Basic wrote:
>> I'm curious to find out what was the reasoning to make Maybe?
>> What is the added value with introducing it?
>> In which situations the above substitution does not hold?
>
> 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?
>
> How should you know that the string doesn't contain something relevant?
>
>
> Greetings,
> Daniel
> _______________________________________________
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
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