[Haskell-cafe] Confused about type seen in the wild

I'm using the yesod-markdown package as a "template" for making my own yesod-mathjax package. I'm pretty much done, and it does compile now, but I'm just really confused by a type that looks like bad syntax. In fact, I ended up trying to "fix" it, which lead to errors: mathJaxField :: Monad m => RenderMessage (HandlerSite m) FormMessage => Field m MathJax Notice that there are two type arrows (=>). Interestingly, mathJaxField :: ( Monad m , RenderMessage (HandlerSite m) FormMessage ) => Field m MathJax compiles too. So it looks like currying/uncurrying, at the type level. But when did this start? I'm using GHC 7.6.3