Couldn't agree more. I see this as just another example of how ordinary function composition usually wins out over OOP. Additionally, AFAICT Promise-like thing

Couldn't agree more. I see this as just another example of how ordinary function composition usually wins out over OOP. Additionally, AFAICT Promise-like things aren't actually used very much in Haskell in practice; at least not in the code I tend to see/write. MVar is probably the nearest direct equivalent, modulo error handling (which would probably just be handled using an Either in an MVar). Given that the runtime is M:N threaded, there doesn't seem to be much need for Promise and its ilk, since you can just do ordinary function composition and HoFs (with channels for communication). If you want something fancy you just use the marvellous "async" library.