Erik Hesselink hesselink at gmail.com
Wed Aug 7 19:13:06 CEST 2013

> Ivan Lazar Miljenovic wrote:
>> If we're starting to add functions to Data.Either, I've often used
>> something like this:
>> mapEither :: (l -> l') -> (r -> r') -> Either l r -> Either l' r'
>> mapEither fl fr = either (Left . fl) (Right . fr)

This function is hidden in Control.Arrow as (+++).

There are more useful functions in there, but it's sometimes hard to
find them, especially now that we can no longer use type operators for
type variables.


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