[Haskell-cafe] Why Maybe exists if there is Either?
Hannes_E at gmx.de
Thu Jan 9 15:07:48 UTC 2014
to keep programs clear, short and simple. What makes you choose String
as type to replace Nothing?
On 09/01/2014 14:50, Vlatko Basic wrote:
> Hello Cafe,
> With my current knowledge of Haskell, I do not see why is there Maybe
> if we have Either.
> For example, Functor and Monad instances (and many others) of Maybe
> and Either are the same (except for fail).
> In other words, this should hold:
> Maybe a = Either String a -- String or something else
> Nothing = Left ""
> Just a = Right a
> 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?
> Best regards,
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
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