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.
The documentation says "There should be more documentation, but there
isn't (yet). Yell if you need it." :)
But I think I was able to understand everything from
the examples.
Thanks.
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