Experimenting with Control.Lens.At and "non"

gistfile1.txt

ghci> at 1 ?~ "hello" $ M.empty
fromList [(1,"hello")]
ghci> at 1 .~ (Just "hello") $ M.empty
fromList [(1,"hello")]
ghci> at 1 .~ Nothing $ M.fromList [(1,"blah")]
fromList []
ghci> (%~) (at 2) (maybe (Just "b") (\x -> Just $ x ++ "bbb")) (M.fromList [(2,"a")])
fromList [(2,"abbb")]

ghci> Nothing ^. non 0
0

ghci> M.empty & at "hello" . non M.empty . at "world" .~ Just "!!!"
fromList [("hello",fromList [("world","!!!")])]


-- Beware, this in a bad use of "non"
ghci> M.fromList [("hello",0)] & at "hello" . non 0 %~ (const 0)
fromList []
-- Beware, this in a bad use of "non"
ghci> M.fromList [("hello",M.empty)] & at "hello" . non M.empty . at "world" .~ Just "!!!"
fromList [("hello",fromList [("world","!!!")])]