Polymorphism and higher order functions

Until now, we've played with functions that operate on only one type of data (monomorphic functions). Now, we will finally apply our type system knowledge to build functions that work for multiple types. Functions that take type parameters are called polymorphic functions similar to polymorphic methods implemented in an object-oriented hierarchy of classes (subtype polymorphism). For functions in Scala, it is called parametric polymorphism.

Polymorphic functions

We have already used polymorphic functions when we played with Glass examples in the previous chapter:

sealed trait Glass[+Contents]
case class Full[Contents](c: Contents) extends Glass[Contents]
case object EmptyGlass...