[dwohnitmok]

You've discovered transducers (which I think have a rather horrible and confusing for newcomers higher-order function presentation in the language that popularized them, i.e. Clojure, when they could just be lists)! All transducers are is a function `x -> List(x)` and then you can use other functions such as `flatMap` to apply them (as your example illustrates nicely this is why map, filter, and its combination can all be described as single transducers).

You do have to make sure that your implementation of list is extremely efficient on zero and one element lists (ideally it generates no garbage at all in those cases) otherwise as other commentators have pointed out you'll have a lot of GC pressure.

And even though the transducer itself is `x -> List(x)` note that the `List` is only produced as an intermediate step and doesn't need to exist in the final product. You could apply a `x -> List(x)` to a generator for example and just "absorb" the list back into the resulting generator.