Lambdas

1

1 Why it doesn't compile? val sum = {x, y -> x + y} println(sum(1,2)) code from http://confluence.jetbrains.net/display/Kotlin/Function+literals is there any plan for local type inference for lambdas?

2 What benefits from local functions
fun main(args:Array<String>){
  val sum = {(x : Int, y : Int) : Int -> x + y}
  fun sum2(x:Int, y:Int):Int {return x + y}
}
if language already have lambdas?

2

1. Seems to be a bug in the docs. Thanks BTW, what type would you expect 'sum' to be?

  1. This makes the language more regular: I can have a function anywhere I like.
    Your argument can be extended to “why have functions at all when we can have val’s of function types?”, and this approach does not seem right.

3

1) Int -> Int Nemerle, for example, have this feature, type inference by usage. def sum(x,y) { x + y } doesn't compile but if local function is used sum(1,2)  it's clear what type it has

4

Nemerle's type inference is indeed very powerful (and, as a consequence, rather slow). Kotlin aims for a simpler (faster and more predictable) type inference algorithm.

5

fun <T,K,R> Tuple2<T,K>.apply(func: Function2<T,K,R>) : R {   return  func(this._1, this._2) }

Is it really

val sum = {x, y -> x + y}
sum(1,2)

more complex then current type inference?

val r =#(1,2).apply({x,y -> x + y})

Local functions are changed often, is’t annoying change it’s type every time.

6

Yes, it is much more complex, because instead of a single call expression we have to analyze the whole local scope.