How to chain vavr's Either nicely?

I have a function returning an Either<MyError, String> (function2) , which result depends on another function returning another Either<MyError, SomethingElse> (function1)
Both functions rely on a Try block that could fail, and I want to compose those two first function to create a "handle" which will be the main function of my class.

There are basically 3 scenarios possible :

function1 fails : I want handle to return the error given by function1
function1 succeeds and function2 fails : function2 must return its own error then returned by handle
both functions work : handle must return the String

Here is my current code :

private Either<MyError, Path> getPath(Arg arg) { // function 1
  return Try.of(() -> //some code that can fail)
              .toEither().mapLeft(e -> new MyError("Error message for function1", e));
}

private Either<MyError, String> getContent(Path path) { // function 2
  return Try.of(() -> //some code that can fail)
              .toEither().mapLeft(e -> new MyError("Error message for function2", e));
}

public Either<MyError, String> handle(Arg arg) {
  return Either.right(arg)
                .map(this::getPath)
                .map(this::getContent);
}

Everything works except the Handle function, I think that my problem might be related to the use of Either::map function, that might not be the thing for my case.

Any thought about this ?

Also, sorry if the answer seems obvious, i am quite new to functionnal programming and vavr.

Solution

The method that could help to make this work would be flatMap.

So if you use flatMap instead of map, the handle method will become something like:

public Either<MyError, String> handle(Arg arg) {
    return Either.<MyError, Arg>right(arg)
        .flatMap(this::getPath)
        .flatMap(this::getContent);
}

The scenarios you mentioned are all covered with this flatMap method.

See the Either.flatMap documentation for the official docs about it.