Undefined at the type level

Question

Often when I\'m playing with Haskell code, I stub things out with a type annotation and undefined.

foo :: String -> Int
foo = undefined
         


        

Answer 1

You can use EmptyDataDecls to stub out a type, and with KindSignatures you can give it a kind:

{-# LANGUAGE EmptyDataDecls, KindSignatures #-}

data Foo :: * -> *

You can also stub out the Monad instance without warnings with this option to GHC.

{-# OPTIONS_GHC -fno-warn-missing-methods #-}

instance Monad Foo

And then you don't need to leave any implementation for return and >>=.