Mastering Functional Programming

Partial functions

The preceding pattern matching statements are very close to the notion of partial functions in Scala. The same way pattern matching statements have a certain domain of cases that they can handle and throw an exception in all other cases, partial functions are defined on a part of their input domain. For example, the preceding match statement can be converted into a partial function, as follows:

scala> val findSquare: PartialFunction[Any, Int] = {     | case x: Int => x * x     | case square(s) => s     | }findSquare: PartialFunction[Any,Int] = <function1>scala> findSquare(2)res12: Int = 4scala> findSquare(new Dummy(3))res13: Int = 9scala> findSquare("Stuff")scala.MatchError: Stuff (of class java.lang.String) at scala.PartialFunction$$anon$1.apply(PartialFunction.scala:255) ...