Proposal: merge either into transformers

Chris Wong lambda.fairy at
Mon Jan 2 07:36:18 UTC 2017

A couple of these are in transformers already.

> Combinators which I am used to using at work include:
>    firstEitherT :: Functor m => (x -> y) -> EitherT x m a -> EitherT y m a

>    secondEitherT :: Functor m => (a -> b) -> EitherT e m a -> EitherT e m b

This is just fmap

Chris Wong (

"I had not the vaguest idea what this meant and when I could not
remember the words, my tutor threw the book at my head, which did not
stimulate my intellect in any way." -- Bertrand Russell

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