I would like to propose export Fix, Free, and Cofree from a new module in base (maybe something like Data.Functor.Recursion, the name is unimportant). The definitions of Free and Cofree would be as there are in the `free` package in Control.Monad.Free and Control.Monad.Cofree. The `free` package would then reexport these types in their respective modules rather than redefining them. All of the other utilities functions from these packages would not be moved to `base`; they would remain in `free`. Fix would be defined as: newtype Fix f = Fix { unFix :: f (Fix f) } The advantage this offers is that Free and Cofree would be able to enjoy a greater number of typeclass instances provided libraries across the ecosystem. As it stands, adding the somewhat heavy `free` dependency is not a good choice for libraries like `aeson`, `mustache`, and `hashable`. In the case of Fix, the ecosystem currently lacks a canonical library that provides it (recursion-schemes and data-fix both offer the same definition though, and various tutorials all define it the same way). It could benefit from the new instances as well. The disadvantage is the usual disadvantage: Adding any data type to base is a future commitment to that data type, and compile times for base go up a little, and there is work to be done to move it into base to begin with. I would gladly help with any of the work that needs to be done to make this happen. I believe that Fix and Free (and Cofree to a lesser extent) have proved themselves over years of use in the ecosystem. I would appreciate any feedback or thoughts that others have on this topic. Thanks. -- -Andrew Thaddeus Martin