Re: [Haskell-beginners] GHC 6.12, -fwarn-unused-do-bind and Text.Printf

On Mon, Feb 22, 2010 at 11:02 PM, Iustin Pop wrote:

A side question would be why we have "instance PrintfType (IO a)" instead of "instance PrintfType (IO ())"; what use is there for that generic type? Can printf return anything else than IO () (when used under IO at all)?

I can only guess, but perhaps because "instance PrintfType (IO ())" would require the FlexibleInstances language extension. I believe the current implementation of printf is fully Haskell98.