A compiled ML function specifically transmitting values from Isabelle to Scala.

The function is created by val f = MLRetrieveFunction(ml) where ml is ML code of type a -> data, and a is the ML type corresponding to A.

When f(mlVal : MLValue[A]) is invoked in Scala, the compiled ML function ml is applied to the ML value of type a referenced by mlVal in the object store in the Isabelle process. The result (of ML type data) is then transferred back to Scala and returned (in a Future).

An MLRetrieveFunction is particularly useful for writing retrieve methods when writing an MLValue.Converter.

The behavior of an MLRetrieveFunction[A] is very similar to an MLFunction[A,Data] but more efficient. And the MLRetrieveFunction additionally does not access the store and retrieve functions of the converter that is passed as an implicit argument. This is important because we use the MLRetrieveFunction for writing those functions in the first place.