How to mix PartialFunction input parameter with output

Question

What is the best way to mix a function input parameter with the output.

Here is my current code :

def zip[A,B](f: A => B) : A => (A, B) = (a: A) => (a, f(a))
def zip[A,B](pf: PartialFunction[A,B]) : PartialFunction[A, (A, B)] = { 
  case a if pf.isDefinedAt(a) => (a, pf(a)) 
}

Is there a better way ? Is there a better naming for that ?

Not really an answer, but with Scalaz's arrow this would just be `identity[A] _ &&& f`. — Travis Brown, Mar 11 '15 at 14:55
@SarveshKumarSingh With better type inference it would just be `id &&& f`, which I think is pretty clear—it just says "apply both of these functions to the same argument and pair the results". — Travis Brown, Mar 11 '15 at 15:05

Ben Reich · Answer 1 · 2015-03-11T22:06:44.890

If you lift then match, you only have to evaluate pf once (unlike in your solution, which evaluates twice):

def zip[A,B](pf: PartialFunction[A,B]): PartialFunction[A, (A, B)] = 
    x => pf.lift(x) match { case Some(res) => x -> res }

Or you can use unlift which takes a function to Option and returns the equivalent PartialFunction:

def zip[A,B](pf: PartialFunction[A,B]) = Function.unlift((x:A) => pf.lift(x).map(x -> _))

How to mix PartialFunction input parameter with output

1 Answers1