[Haskell-cafe] Problem with existential type and instance.

Magicloud Magiclouds magicloud.magiclouds at gmail.com
Mon Jul 28 05:46:53 UTC 2014


  For code like below, how to make it compilable?

data EventHandlers = forall m. MonadIO m => EventHandlers { onDeleteWindow
:: Maybe (m ()) }
instance Default EventHandlers where
  def = EventHandlers Nothing


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