Scala:(Int,Int)=> Int不匹配(Int,Int)=> Int

Question

我正在尝试使用y-combinator在scala中定义gcd:

object Main {
  def y[A,B]( f : (A => B) => A => B ) : A => B = f(y(f))
  def gcd = y[(Int,Int),Int]( (g) => (x,y) => if (x == 0) y else g(y % x, x) )
}

但我收到一个错误:

Main.scala:3: error: type mismatch;                                                  
 found   : (Int, Int) => Int                                                               
 required: (Int, Int) => Int                                                               
    def gcd = y[(Int,Int),Int]( (g) => (x :Int,y :Int) => if (x == 0) y else g(y % x, x) ) 
                                                       ^

如果我讨论所有的论点,那就没有问题:

def gcd = y[Int,Int => Int]( g => x => y => if (x == 0) y else g(y % x)(x) )

在未经证实的版本中,我做错了什么？

Answer 1

有点(g) => (x :Int,y :Int) =>.Scala期望你的参数是(Int,Int)的元组,所以它会更像(g) => (tup: (Int, Int)) =>

您可以使用一些模式匹配来避免在tup上使用_1和_2匹配.这对我来说很好:

def gcd = y[(Int, Int), Int](g => {
  case (x,y) => if(x == 0) y else g(y % x, x)
})