monad example in Monte using control blocks

monad_example.mt

exports (main)

def id(x) as DeepFrozen:
    return x

object identity as DeepFrozen:
    "The identity monad."

    to unit(x):
        return x

    to "bind"(action, f):
        return f(action)

    to control(operator :Str, argArity :Int, paramArity :Int, block):
        return switch ([operator, paramArity]):
            match ==["do", 1]:
                # The inner value and our action upon it.
                def [[value], lambda] := block()
                object controller:
                    to control(operator, argArity, paramArity, block):
                        def [_, nextLambda] := block()
                        def identityBlock():
                            return [[value], fn x, ej {
                                nextLambda(lambda(x, ej), ej)
                            }]
                        return identity.control(operator, argArity,
                                                paramArity, identityBlock)

                    to controlRun():
                        return lambda(value, null)
            match msg:
                throw(`Unrecognized control operator $msg`)

def main(_) as DeepFrozen:
    traceln(identity (2) do x { x + 3 } do y { y + 3 })