[Haskell-beginners] "Learn You a Haskell" question

[Frank]

Thanks!

On Monday, August 18, 2014, Bob Ippolito <bob at redivi.com> wrote:

> The definition of a Functor requires that exactly one of the type
> variables be free, which is why it's written as `Either a` instead of
> `Either a b`. Any fields that are not `b` must be simply passed through
> as-is by fmap. There could be a separate functor that would fmap over the
> Left, but there isn't (in the base package anyhow).
>
> There's a related Functor for `(,) a` where the Functor fmaps over the snd
> of the tuple, and the fst is left as-is.
>
> fmap (+1) ('a', 2) == ('a', 3)
> fmap (+1) (Right 2) == Right 3
> fmap (+1) (Left 'a') == Left 'a'
>
> Chris Done recently prototyped a fmap explorer that you might find useful:
> http://www.reddit.com/r/haskell/comments/2dok9w/functor_explorer/
>
> -bob
>
>
>
> On Mon, Aug 18, 2014 at 11:02 AM, Frank <frankdmartinez at gmail.com
> <javascript:_e(%7B%7D,'cvml','frankdmartinez at gmail.com');>> wrote:
>
>> Hi,
>>     I'm reading "Learn You a Haskell..." and have a question about the
>> chapter "Making Our Own Types and Typeclasses". On the 'Functor'/'Either'
>> example, I feel completely lost. I don't see why the 'Left x' portion of
>> 'Functor (Either a)' is simply 'Left x' and the document is not exactly
>> clear. Any clarification would be most appreciated.
>>
>> Sincerely,
>> Frank D. Martinez
>>
>>
>> --
>> P.S.: I prefer to be reached on BitMessage at
>> BM-2D8txNiU7b84d2tgqvJQdgBog6A69oDAx6
>>
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>>
>

-- 
P.S.: I prefer to be reached on BitMessage at
BM-2D8txNiU7b84d2tgqvJQdgBog6A69oDAx6
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