deriving-ord.hs

data Position = Position
    { _x :: Integer
    , _y :: Integer
    } deriving (Show, Eq)

-- We want to sort by Y first, and then by X, so we need a custom Ord instance
instance Ord Position where
    Position x0 y0 <= Position x1 y1 =
        if y0 /= y1
            then y0 <= y1
            else x0 <= x1

-- Or we can rearrange the internal structure of our Record
data Position' = Position'
    { _y :: Integer
    , _x :: Integer
    } deriving (Show, Eq, Ord)