I'm trying to use the y-combinator to define gcd in scala:
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) )
}
But I'm getting an error:
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) )
^
If I curry all the arguments, then there's no problem:
def gcd = y[Int,Int => Int]( g => x => y => if (x == 0) y else g(y % x)(x) )
What am I doing wrong in the uncurried version?
The bit with
(g) => (x :Int,y :Int) =>
. Scala expects your argument to be a tuple of (Int,Int), so it would be more like(g) => (tup: (Int, Int)) =>
You can use a bit of pattern matching to avoid having to use
_1
and_2
matching on tup. This compiles just fine for me: