On Mon, 18 Jan 2016, Ryan Scott wrote:
WriterT (and Writer) don't quite capture what I need. With WriterT, you have to tack on that extra m type parameter, and when you just specialize it to Identity, it only serves as an extra hoop to jump through to dig out the state. The prescence of the m type parameter also prevents me from easily modifying the state with a Bifunctor instance, whereas tuples have no such obstacle.
Is it important to achieve this with Bifunctor functions? You could write a state changing function, or add it to 'transformers', or define your own Writer as an independent type like it was in mtl initially.
It's a minor difference, but an important one when I decide which data structure to reach for.
Sure, but if you want a certain behaviour then a custom type is better than putting so much overloading to a standard (tuple) type, isn't it?