What's the point of using monads in an interpreter?

Question

I recently discovered this little scala example called Simple interpreter using monads:

object simpleInterpreter {

  case class M[A](value: A) {
           


        

Answer 1

Using a monad makes the parser/interpreter extensible. This paper by Philip Wadler takes some time to read, but explores this idea in great detail. See also Monadic Parsing in Haskell.