[Haskell-beginners] Question about class declaration

[Rafael Gustavo da Cunha Pereira Pinto]

Hi folks,

Once in a while I stumble upon declarations like this:

class EditAction e a | e -> a where
  apply :: a -> e -> a



Why is the vertical bar there? I understand that => defines a context, but
can't find what is the "|" for.


Thanks


Rafael Gustavo da Cunha Pereira Pinto
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