On 5 March 2017 at 21:51, Vladislav Zavialov
Since 'Data.List.NonEmpty' is now in 'base', it makes sense to change the type of 'some' from
some :: Alternative f => f a -> f [a]
to
some :: Alternative f => f a -> f (NonEmpty a)
as it's guaranteed to return a non-empty list.
Currently, both users and implementors of 'Alternative' instances are at a disadvantage. The users have to use the unsafe NonEmpty.fromList function to take advantage of the fact that the result of 'some' is indeed non-empty. The implementors have more space for error - it's possible to accidentally return an empty list.
The disadvantage is also for people trying to maintain a code base, though that's solvable with CPP if needed. However, this also affects the default instances. (As a user and implementor of Alternative instances, I've never found myself at a disadvantage for using the current type.)
I volunteer to implement. Does everyone agree it's a good idea?
I'm -0.5. -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com http://IvanMiljenovic.wordpress.com