Functor, Applicative, Monad, Foldable, Traversable instances for (, , ) a b

Henning Thielemann lemming at
Thu Mar 30 20:06:23 UTC 2017

On Thu, 30 Mar 2017, Nathan Bouscal wrote:

> The argument that people should define custom data types rather than 
> using triples doesn't have any bearing on whether triples should 
> implement these type classes. That argument would imply that whether the 
> type classes are implemented doesn't matter, because if you're 
> complaining about getting unexpected results the response is "use a 
> custom data type",

I don't want unexpected results, I want clear type errors. That's only 
possible with missing type instances.

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