Scala Monad - Full worked example [closed]

Answer 1

All collections are monads (that's a general statement, not a Scala-specific one), or "have monads" depending on how strict you want to be about it. Scala also has Option as a monad, and the right and left projections of Either as well. You can see their monadic aspects at work whenever you see a for-comprehension with them.

A more subtle example of monads in Scala is the parser combinators. It is more subtle because the operators hide the monadic operations behind synonyms that look better in a grammar.

Answer 2

see http://jazzy.id.au/default/2012/11/02/scaling_scala_vs_java.html

Eg async call using monads to four clients:

for {
  user <- getUserById(id)
  orders <- getOrdersForUser(user.email)
  products <- getProductsForOrders(orders)
  stock <- getStockForProducts(products)
} yield stock

Futues are monadic and for comprehensions can be used to compose asynchronous code

In java well... start waiting Monads with Java 8

Answer 3

def optionAdd(x:Option[Int], y:Option[Int]):Option[Int] = 
  for(xx <- x; yy <- y) yield xx+yy 

I don't dare wasting time with the java version, specially because someone greatly smarter than me already did http://functionaljava.org/examples/1.5/#Option.bind. The example in link is doing basically what optionAdd does in a infinitely less concise way.