[Haskell-beginners] Re: Either Monadic Trouble
iaefai at me.com
Mon Nov 9 18:05:04 EST 2009
This is all very confusing. You say that it is defined in the
transformers. Does this mean it is possible to use the code I am
trying to get to work to do what I want?
You also mention the attempt package, I must admit that I am not
entirely sure how to use it either. Note that I haven't done a lot of
error handling in haskell (the extent usually involved Maybe)
On 2009-11-09, at 4:00 PM, Nicolas Pouillard wrote:
> Excerpts from Ertugrul Soeylemez's message of Mon Nov 09 21:44:44
> +0100 2009:
>> Nicolas Pouillard <nicolas.pouillard at gmail.com> wrote:
>>>> Either is not a monad, you can check this by typing
>>>> :i Either
>>>> in GHCi; you will not see a line like
>>>> instance Monad Either
>>>> in the result. Compare this to
>>>> :i Maybe
>>> In fact the Either Monad instance is defined in the
>>> 'transformers' (or
>>> 'mtl') packages.
>> Either is still not a monad. Have a look at its kind.
> OK, right Either is not but (Either e), where e must be in
> the Error type class.
> Nicolas Pouillard
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