Making a partial function complete

user_2072459 0
Viewed 108

Is there a standard way to complete a partial function PartialFunction[A, B]? Something like this:

completePartialFunction(pf: PartialFunction[A, B], z: B): A => B

or

completePartialFunction2(pf: PartialFunction[A, B], f: A => B): A => B
scala functional-programming
4 Answers

You can use lift method on PartialFunction, that returns Option[B]. So when the function is not defined for the input, None is returned. You can find more in the scaladocs.

Other solution that comes to my mind is when you're using cats or scalaz. You can then check whether the function is defined for the argument and when not, return empty from the Monoid[B] that you should pass (probably implicitly) to completePartialFunction.

user_76067640

Yes, it's actually very simple:

  def complete[A, B](pf: PartialFunction[A, B])(f: A => B): A => B =
    pf.applyOrElse(_, f)
user_55820280

If I understand the question, you want to use f() to supplement pf() so that all possible values of type A are covered.

def completePartialFunction2[A,B](pf : PartialFunction[A,B]
                                 ,f  : A => B): A => B =
  (a:A) => if (pf.isDefinedAt(a)) pf(a) else f(a)
user_49931280

Another simple version:

def completePartialFunction[A, B](pf: PartialFunction[A, B], f: A => B): A => B
  = pf orElse { case a: A => f(a) }
user_76626700
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