[Haskell-beginners] Help needed in understanding MonadWriter syntax.

[Vinay Emani]

Hi,

I'm trying to understand the MonadWriter class definition syntax. Now, I'm
using GHC 7.6 and the class is defined as

class (Monoid w, Monad m) => MonadWriter w m | m -> w where
    ....

I've never seen '|' in the middle of a class definition, could some one
explain this? It's used in the guard syntax as well as to separate data
constructors in a type definition.

Regards
Vinay
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