Instead of repeatedly calling replaceElement to update the grid, we use the setElement function to update a single cell, and then we process the valid neighbors using a combination of map and filter.

We define a list of neighbors relative to the current cell. In this case, we exclude diagonals (as indicated by dx /= dy) to mimic the original behavior.

We use filter to retain only the valid neighbor positions within the grid bounds.

We recursively call spreadLight for each valid neighbor and update the grid with the light. This is done using foldl and generates a new grid with light spreading efficiently.