lens-op-ob-tolistofexamples.hs

toListOfExamples :: IO ()
toListOfExamples = do
  let tory = HM.fromList [ ("gold", Item 99 10)
                          , ("silver", Item 10 9)
                          ]
      bob = User (UserName "bob") 42 Nothing tory

  print "A list of Bob's items"
  print $ bob ^.. inventory . folded
  -- [Item {_itemValue = 10, _itemWeight = 9},Item {_itemValue = 99, _itemWeight = 10}]
  print $ toListOf (inventory . folded) bob
  -- [Item {_itemValue = 10, _itemWeight = 9},Item {_itemValue = 99, _itemWeight = 10}]

  print "Bob uses ifolded . asIndex to list itemNames."
  print $ bob ^.. inventory . ifolded . asIndex
  -- ["silver","gold"]

  print "Bob's filtering to only his valuable items."
  print $
    bob ^.. inventory . folded . filtered (\item -> (item ^. value) > 50)
  -- [Item {_itemValue = 99, _itemWeight = 10}]