On 2013-08-07 19:13, Erik Hesselink wrote:
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 (+++).
I didn't know about those functions, and it seems everything I wanted is in there somewhere. However, I'm not sure what to think of Control.Arrow, I've always (ab)used it as an extended Data.Tuple, and as of today probably for its Either API functions. The thing is of course that Arrows aren't meant to be *just* that. Maybe there should at least be a highlighted section in Data.Either/Data.Tuple telling the user about the functionality provided in Control.Arrow? Most of the functions proposed here seem redundant, apart from the fact that they're arguably not in the right place. (A specialized re-export might be worth considering too, although I'm not sure whether I'd personally want that.) David