https://twitter.com/chrislpenner/status/1750371021365100670

nerdswipe.hs

newtype Position = (Integer, Integer)
data Replacement = {
    rStart :: Position,
    rEnd   :: Position,
    rText  :: [Char]
}
data Intersect = BEFORE | INSIDE | AFTER

replace :: [Replacement] -> [Char] -> State Position [Char]
replace _ [] = return []
replace [] text = return text
replace (r:rs) (c:cs) = do
    cursor <- get
    modify (updateCursor c)
    case intersect r cursor of
        BEFORE -> do
            rest <- replace (r:rs) cs
            return (c:rest)
        INSIDE -> replace (r:rs) cs
        AFTER -> do
            rest <- replace rs cs
            return (rText r) ++ rest
      
updateCursor :: Char -> Position -> Position
updateCursor c (line, col) =
    if c == '\n' then (line + 1, 0)
                 else (line, col + 1)

intersect :: Replacement -> Position -> Intersect
intersect replacement cursor
    | cursor < rStart replacement = BEFORE
    | cursor >= rEnd replacement = AFTER
    | otherwise = INSIDE