Mauricio wrote:
Hi,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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