[Haskell-cafe] Syntax question: class (Monad m) => MonadReader
r m | m -> r where
andrewcoppin at btinternet.com
Sun Nov 2 08:46:43 EST 2008
> I've reading Control.Monad.Reader source code and
> arrived here:
> class (Monad m) => MonadReader r m | m -> r where
> I can't understand that syntax. Since this is not a
> 'data' line, what is the '|' supposed mean?
It's called a "functional dependency". This is not part of the
Haskell-98 language standard; check the GHC manual.
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