Named typeclasses in Haskell

One of the best features of Haskell are typeclasses. Still, it is not easily possible to have multiple implementation of the same typeclass for the same data type. For example, to define an additive and a multiplicative instance of Monoid on Int, one needs to use specific newtype wrappers such as Sum and Product. On the other hand, in Idris it is possible to define multiple named implementations o

[lotz84]

型クラスに幽霊型を加えてMultiParamTypeClassesにすることでTypeApplicationsでインスタンスを切り替えるテクニック面白いな。個人的にはAllowAmbiguousTypesが必要なところが玉に瑕