Extracting Leaf paths from n-ary tree in F#

Question

Inspired by this question, I wanted to try my hand at the latest ponder this challenge, using F#

My approach is probably completely off course, but in the course of

Answer 1

Regarding laziness - You can make this lazy by using F# "seq" type instead of "list" type. Here is an example:

let rec visitor2 lst tree =
  match tree with
  | Branch(n, sub) -> Seq.map_concat (visitor2 (lst * 10 + n)) sub
  | Leaf(n) ->
      seq { do printfn "--yielding: %d" (lst * 10 + n)
            yield lst * 10 + n };;

The "seq" thing is a sequence expression, which represents a lazy stream of values. I added "printfn" to the code, so we can track how things are executing:

> visitor2 0 tr |> Seq.take 2;;
--yielding: 13
--yielding: 124
val it : seq = seq [13; 124]

You can probably use something like Seq.first to find the first value which represents the result.