How to walk PsiDirectory recursively using provided api

In my custom language(named KCL), if a PsiDirectory contains KCL files recursively, then it can be a KCL package. So I check if a PsiDirectory is a KCL package by doing this:

public static boolean isKCLPackage(PsiDirectory dir) {
    for (PsiFile file : dir.getFiles()) {
        if (file instanceof KCLFile) {
            return true;
        }
    }
    for (PsiDirectory subDir : dir.getSubdirectories()) {
        if (isKCLPackage(subDir)) {
            return true;
        }
    }
    return false;
}

Is there a better way or some API to walk the file tree recursively? for example, I see Java 8 provides a stream to process all files in a tree to traverse files:

Files.walk(Paths.get(path))
        .filter(Files::isRegularFile)
        .forEach(System.out::println);

Any help/pointers are gratefully received.