[Haskell-beginners] class (Monad m) => MonadState s m | m -> s where - What does m | m -> s construct do?

[Amitava Shee]

I can across the following construct in ghc source

class (Monad m) => MonadState s m | m -> s where
    get :: m s
    put :: s -> m ()

I am not aware of the syntactic construct  | m -> s just before the where?
Can someone please explain it?


Thanks & Regards,
Amitava Shee
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