Re: [Haskell-cafe] Implementing ParseChart with Data.Map

Duncan Coutts wrote:

modify :: k -> Map k e -> (e, Maybe e -> Map k e)

so it's a lookup that returns the element at k and also a continuation that lets you rebuild a new map with an altered element. I guess that doesn't account for the element not existing. There's probably a generalisation that does.

isn't it just adding the necessary Maybe?: modify :: k -> Map k e -> (Maybe e, Maybe e -> Map k e) ? -Isaac