为什么在Scala中的匿名函数内不能有for循环？

Question

when I try to run the following code:

val anonFunc = (x: Pos): List[Pos] => {for(i <- 1 to 10){ println(i)}

I get the following error:

 illegal start of declaration

and I have no idea why. This code is used inside a function

Answer 1

(1) There two ways to ensure correct return type of anonymous function that I know:

val f = (x: Int) => { x + 1 }: Double

val f: Int => Double = x => x + 1

(2) Your for comprehension will return Unit as it's written, not List[Pos] . To return something real you need to use yield :

val anonFunc = (x: Pos) => { for(i <- 1 to 10) yield(x) }: List[Pos]

but as you do this you will notice that compiler doesn't like List as a return type because what for returns is IndexedSeq , not List . So you need to convert it explicitly:

val anonFunc = (x: Pos) => { for(i <- 1 to 10) yield(x) }.toList: List[Pos]