Question

2b

Please code in language: Ocaml

TODO: Implement a recursive OCaml function ascending : int -> int list, which accepts an integer n as input (again, assume n ≥ 0), and returns a list of integers from 0 to n in ascending order.

starter code:

let ascending (n : int) : int list = (* your work here *) [ ]

Answer 1

Below program returns the list of integers within the range a and b, if a > b then list is displayed in descending order. For the given question use a=0 and b=N.

# let range a b =
    let rec aux a b =
      if a > b then [] else a :: aux (a+1) b  in
    if a > b then List.rev (aux b a) else aux a b;;
val range : int -> int -> int list = <fun>

A tail recursive implementation:

# let range a b =
    let rec aux acc high low =
      if high >= low then
        aux (high::acc) (high - 1) low
      else acc
    in if a < b then aux [] b a else List.rev (aux [] a b);;
val range : int -> int -> int list = <fun>

Output

# range 4 9;;
- : int list = [4; 5; 6; 7; 8; 9]
# range 9 4;;
- : int list = [9; 8; 7; 6; 5; 4]