Desugaring various for-expressions in Scala

desugar.scala

/** EXAMPLE 1
  * From the 2015 Scala final, exercise 3
  * http://lamp.epfl.ch/files/content/sites/lamp/files/teaching/progfun/prev-exams/final-2015.pdf
  */
// For-expresion
for {
  msg <- acc
  msg2 <- doAction(elem)
} yield {
  msg ++ List(msg2)
}

// Desugared
acc flatMap { msg => 
  doAction(elem) map { msg2 =>
    msg ++ List(msg2)
  }
}

/** EXAMPLE 2
  * From the 2014 Scala final, exercise 1
  * http://lamp.epfl.ch/files/content/sites/lamp/files/teaching/progfun/prev-exams/final-2014.pdf
  */
// For-expression
for (m <- movies) yield
  m.title + ", directed by " + m.director + " (" + (2014 - m.releaseDate) + " years ago)"
// Desugared
movies map { m =>
  m.title + ", directed by " + m.director + " (" + (2014 - m.year) + " years ago)"
}

// For-expression
for {
  m <- movies
  if m.leadActors contains "Philip Seymour Hoffman"
} yield m.title
// Desugared
movies
  .filter((m: Movie) => m.leadActors contains "Philip Seymour Hoffman")
  .map((m : Movie) => m.title)

// For-expression
for {
  m1 <- movies
  director = m1.director
  m2 <- movies
  if m2.leadActors contains director
} yield (director, m2.title)
// Desugared
movies flatMap { m1 =>
  val director = m1.director
  movies
    .filter(_.leadActors contains director)
    .map { m2 => (director, m2.title) }
}