From flatMap to

do-Notation

Hamburg Haskell Meetup

Aug 24, 2016

function duplicate(n) {
  return [n, n];
}

_.flatMap([1, 2], duplicate);
// ➜ [1, 1, 2, 2]

JavaScript: lodash for collections

Java: Optional

Optional<Int> foo = Optional.of(3);
// Optional<Int> foo = Optional.empty();
Optional<Int> bar = foo.flatMap(n -> {
  if (even(n)) {
    return Optional.of(n + 1);
  } else {
    return Optional.empty();
  }
});