literal translation of https://doc.rust-lang.org/rust-by-example/std/result.html .. not type checked, for illustration purposes only

MathError.hs

data MathError
  = DivisionByZero
  | NonPositiveLogarithm
  | NegativeSquareRoot
deriving Show

type MathResult = Either MathError Double

div :: Double -> Double -> MathResult
div x y =
  if y == 0
    then Left DivisionByZero
    else Right(x / y)
    
sqrt :: Double -> MathResult
sqrt x =
  if x < 0
    then Left NegativeSquareRoot
    else Right (x ** 0.5)
    
ln :: Double -> MathResult
ln x =
 if x <= 0
  then Left NonPositiveLogarithm
  else Right (Math.log10 x)

-- op x y == sqrt(ln(x/y))
op :: Double -> Double -> MathResult
op x y = do
  ratio <- div x y
  ln' <- ln ratio
  sqrt' <- sqrt ln'
  return sqrt'
  
main :: IO ()
main = do
  case (op 1 10) of
    Left why -> throwError (show why)
    Right res -> print res

-- The `Either` type is provided by the standard library as
-- data Either a b = Left a | Right b

Notice how op's definition isn't full of nested case statements.. the nesting logic is handled internally by the Either monad.. any time you see a do statement that means you've encountered monadic code