[Haskell-cafe] instance Alternative (Either [a])
john at repetae.net
Thu May 22 04:28:15 UTC 2014
I use a similar idiom
newtype P b a = P ([b],Maybe a)
Note that the [b] is _outside_ the maybe (or either), this means that
the accumulated value can be propagated through failure.
Notably, <*> and `ap` have very different meanings for this which is
not true for other monads. <*> will collect [b] from both sides while
`ap` will only do the left.
On Wed, May 21, 2014 at 9:18 PM, Kim-Ee Yeoh <ky3 at atamo.com> wrote:
> On Thu, May 22, 2014 at 6:58 AM, Tony Morris <tmorris at tmorris.net> wrote:
> I don't understand how to use this package.
> Is it because Either is an ugly name for the data type and Validation is
> And AccValidation is to be used over Validation, like in Hungarian notation,
> to indicate (the possibility of?) a Semigroup instance on Left / Failure?
> -- Kim-Ee
John Meacham - http://notanumber.net/
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