在 Scala 中组合部分函数

Question

我有两个偏函数f1和f2我想将它们组合成一个新的偏函数f以便f.isDefinedAt(x) iff f1.isDefinedAt(x) || f2.isDefinedAt(x)。我的意思是

        --
       | f1(x) iff f1.isDefinedAt(x)  
       |
f(x) = |
       |
       | f2(x) iff  !f1.isDefinedAt(x) && f2.isDefinedAt(x)  
        --

有没有办法以这种方式组成f1和f2？

Answer 1

在PartialFunction上使用方法.orElse：

scala> val f1: PartialFunction[Int, Unit] = { case x if x > 0 => println(s"called f1 with $x") }
f1: PartialFunction[Int,Unit] = <function1>
scala> val f2: PartialFunction[Int, Unit] = { case x if x < 0 => println(s"called f2 with $x") }
f2: PartialFunction[Int,Unit] = <function1>
scala> (f1 orElse f2)(1)
called f1 with 1
scala> (f1 orElse f2)(-1)
called f2 with -1
scala> (f1 orElse f2)(0)
scala.MatchError: 0 (of class java.lang.Integer)
  at scala.PartialFunction$$anon$1.apply(PartialFunction.scala:253)
  at scala.PartialFunction$$anon$1.apply(PartialFunction.scala:251)
  at $anonfun$1.applyOrElse(<console>:11)
  at $anonfun$1.applyOrElse(<console>:11)
  at scala.runtime.AbstractPartialFunction$mcVI$sp.apply$mcVI$sp(AbstractPartialFunction.scala:36)
  at scala.runtime.AbstractPartialFunction$mcVI$sp.apply(AbstractPartialFunction.scala:36)
  at scala.runtime.AbstractPartialFunction$mcVI$sp.apply(AbstractPartialFunction.scala:28)
  at $anonfun$1.applyOrElse(<console>:11)
  at $anonfun$1.applyOrElse(<console>:11)
  at scala.PartialFunction$OrElse.apply(PartialFunction.scala:167)
  at scala.Function1$class.apply$mcVI$sp(Function1.scala:36)
  at scala.PartialFunction$OrElse.apply$mcVI$sp(PartialFunction.scala:164)
  ... 32 elided

Answer 2

使用 PartialFunction 的 orElse

f1 orElse f2