The state of the art is the amazing `lens` package https://github.com/ekmett/lens/wiki/Overview https://github.com/ekmett/lens/wiki/Overview . See this example,

The state of the art is the amazing `lens` package https://github.com/ekmett/lens/wiki/Overview https://github.com/ekmett/lens/wiki/Overview . See this example, https://github.com/ekmett/lens/blob/master/examples/Pong.hs https://github.com/ekmett/lens/blob/master/examples/Pong.hs