Question

I wonder if there is some function in the F# libraries similar to this one?

let map_acc (f:int->int) (list:int list) =
  let rec map_acc' f acc = function
    | []   -> []
    | h::t -> (f (h+acc))::(map_acc' f (h+acc) t)
  map_acc' f 0 list

Usage:

let xxx = map_acc id [1..10]

val xxx : int list = [1; 3; 6; 10; 15; 21; 28; 36; 45; 55]

Its purpose is quite similar to map‘s but it passes the current state (in the given case, an accumulator) to each element of the list.

Answer 1

Yes, List.scan is the missing key you seek:

[1..10]
|> List.scan (+) 0
|> List.tail //skip the seed value, 0
|> List.map id //of course, map id is not useful, but just illustration here