identity-element.scala

val a: List[Int] = Nil
a: List[Int] = List()

scala> a map {x => x + 2 }
res0: List[Int] = List()

scala> val a = Nil
a: scala.collection.immutable.Nil.type = List()

scala> a map {x => x + 2 }
<console>:13: error: value + is not a member of Nothing
       a map {x => x+2 }
                    ^

scala> val a: List[String] = Nil
a: List[String] = List()

scala> a map {x => x + "2" }
res2: List[String] = List()


scala> val a:Option[Int] = None
a: Option[Int] = None

scala> a.get
java.util.NoSuchElementException: None.get
  at scala.None$.get(Option.scala:349)
  at scala.None$.get(Option.scala:347)
  ... 29 elided

scala> a map {x => x + 2 }
res10: Option[Int] = None

scala> val a:Option[Int] = Some(5)
a: Option[Int] = Some(5)

scala> a map {x => x + 2 }
res11: Option[Int] = Some(7)

scala> import scala.util.Failure
import scala.util.Failure

scala> import scala.util.Success
import scala.util.Success

scala> val a: Try[Int] = Try(5/0)
a: scala.util.Try[Int] = Failure(java.lang.ArithmeticException: / by zero)

scala> a map {x => x+2 }
res0: scala.util.Try[Int] = Failure(java.lang.ArithmeticException: / by zero)

scala> a.foldRight(0)(_ + _)
res10: Int = 10

scala> a.foldRight(1)(_ * _)
res11: Int = 24