This is a quick-and-dirty solver for the "impossible" sudoku at https://cracking-the-cryptic.web.app/sudoku/897LqtfTQD. I recommend trying it yourself or watching one of their excellent videos about the solving experience, starting with this one: https://www.youtube.com/watch?v=yKf9aUIxdb4
Don't look here for clean code or great idiomatic Haskell; I'm no Haskell expert, and was just playing around.