Question 1

Given the list below, use scan to return the intermediate and final cumulative sums.

[ 1; -4; 7; 2; -10]

(0, [ 1; -4; 7; 2; -10])
||> List.scan (fun acc x -> acc + x) 

val it: int list = [0; 1; -3; 4; 6; -4]

Question 2

Given the list below, use fold to return the final sum.

[ 1; -4; 7; 2; -10]

(0, [ 1; -4; 7; 2; -10])
||> List.fold (fun acc x -> acc + x) 

val it: int = -4

Question 3

Given the list below, use mapFold to return the intermediate and final cumulative sums.

[ 1; -4; 7; 2; -10]

(0, [ 1; -4; 7; 2; -10])
||> List.mapFold (fun acc x -> acc + x, acc + x)

val it: int list * int = ([1; -3; 4; 6; -4], -4)

Question 4

Given the list below, use mapFold to return a tuple of

1. A new list in which each element of the original list is transformed by adding 1 to it and then converted into a string.
2. The final cumulative sums of the list elements.

[ 1; -4; 7; 2; -10]

(0, [ 1; -4; 7; 2; -10])
||> List.mapFold (fun acc x -> string (x + 1), acc + x) 

val it: string list * int = (["2"; "-3"; "8"; "3"; "-9"], -4)

Question 5

Given the list below, use mapFold to return a tuple of

1. The list of records with the Y field in each record updated to Y+1
2. The sum of the Y fields.

type R1 = { X : string; Y : int }

let r1xs =
    [ { X = "a"; Y = 1 }
      { X = "b"; Y = -4 }
      { X = "c"; Y = 7 } 
      { X = "d"; Y = 2 }
      { X = "e"; Y = -10 }]

(0, r1xs)
||> List.mapFold (fun acc x -> { x with Y = x.Y+1}, acc + x.Y) 

val it: R1 list * int =
  ([{ X = "a"
      Y = 2 }; { X = "b"
                 Y = -3 }; { X = "c"
                             Y = 8 }; { X = "d"
                                        Y = 3 }; { X = "e"
                                                   Y = -9 }], -4)