Re: [Haskell-cafe] what exactly does "deriving (Functor, Monad, MonadIO)" do?

tphyahoo:

I was trying to follow the reasoning in Don's article on using haskell for shell scripting

http://cgi.cse.unsw.edu.au/~dons/blog/2007/03/10

In the source listing at the end we is

newtype Shell a = Shell { runShell :: ErrorT String IO a } deriving (Functor, Monad, MonadIO)

and I don't understand it what "deriving" is doing here, nor have I been able to find documentation on it.

That's 'cunning newtype deriving, my new favourite ghc language extension. http://www.haskell.org/ghc/docs/latest/html/users_guide/type-extensions.html... We also use it in xmonad, newtype X a = X (ReaderT XConf (StateT XState IO) a) deriving (Functor, Monad, MonadIO, MonadState XState, MonadReader XConf) :-) -- Don