how can I change element on the list?

Question

I have a list (first number is id rectangle, second number is width rectangle, third number is height rectangle):

[Rectangle 1 33 33, Rectangle 2 23 45, Rectangle 3 34 56]

How can I change width and height rectangle with id = 2 ? I don't know how I can implement function modifyRectangle.

My code:

modifyRectangle :: [RectangleType] -> Int -> Int -> Int -> IO [RectangleType]
modifyRectangle [] _ _ _ = return []
modifyRectangle x idRectangle new_width new_height = do
    let (Rectangle id width height) = fromJust (findRectangle idRectangle x)
    -- what next ???????
    return x

findRectangle :: Int -> [RectangleType] -> Maybe RectangleType
findRectangle _ [] = Nothing
findRectangle n ((Rectangle id width height) : xs) =
    if n == id then Just (Rectangle id width height)
    else findRectangle n xs

data RectangleType = Rectangle Int Int Int deriving(Show, Read)

addRectangle :: RectangleType -> [RectangleType] -> [RectangleType]
addRectangle x [] = [x]
addRectangle x xs = x:xs

Answer 1

You can't modify it, you can just make a copy with different values.

there are a number of approches to this, you could filter out the original rectangle and add a new one (won't keep order) or map a function over the original list that returns the passed in rectangle unless the id matches, in which case the new rectangle is returned.