Nested mutable vectors, vector-init with effects and local-var

[burjui]

While porting some small Rust code to koka, I have been struggling with mutating elements of nested vectors. The koka documentation is really sparse, so I had to browse the standard library source to find a way to do it. After stumbling on the [] function and battling with the compiler, I came up with this code:

fun main()
  var v := vector(3, local-new(vector(0, 0)))
  for(0, 2) fn(i)
    v[i] := local-new(vector(5, 0))
  v[2][4] := 666
  println(local-get(v[2])[4])

It works fine, even though it's not as concise as the Rust version. But what bugs me is the need to fill the nested vectors in a loop, while also wasting the vector(0, 0)). I wanted to use vector-init

var v := vector-init(3, fn(_) local-new(vector(5, 0)))

but it requires a lambda without effects. Is it possible to modify vector-init so it allows effects in the lambda and propagates them to the caller?

I couldn't find any docs on local-var and how am I supposed to use it correctly. In the recent discussion on Gitter, someone suggested that a local-var should not escape its lexical scope. This begs the question: what is considered a lexical scope? Is the lexical scope of local-new(vector(5, 0)) the for lambda or the whole function? Is my code correct or is there some compiler bug that I'm unknowingly exploiting here?