printlnfor.scala

for {
  item <- items
  transformed = transform(item)
} yield transformed

// let's say you need a println

def print(a: Any) = { println(a); a }
for {
  item <- items
  transformed = print(transform(item))
} yield transformed

// or 

for {
  item <- items
  _ = println(item) // ignore output
  transformed = transform(item)
} yield transformed