Java can do that trivially easy for the stream case because there is only one input and one output. E.g. static <A, B, X> Function<A, X> compose(Function<A

Java can do that trivially easy for the stream case because there is only one input and one output. E.g. static <A, B, X> Function<A, X> compose(Function<A, B> one, Function<B, X> two) { return (a) -> { return two.apply(one.apply(a)); } } Java sucks when there are a variable number of generic arguments, so it struggles with the composition of two functions that have a variable number of inputs. That doesn't really apply to stream processing though.