Source code in the ocaml programming language

let rec seeAndSay = function
  | [], nys -> List.rev nys
  | x::xs, [] -> seeAndSay(xs, [x; 1])
  | x::xs, y::n::nys when x=y -> seeAndSay(xs, y::1+n::nys)
  | x::xs, nys -> seeAndSay(xs, x::1::nys)


> let gen n =
    let xs = Array.create n [1] in
    for i=1 to n-1 do
      xs.(i) <- seeAndSay(xs.(i-1), [])
    done;
    xs;;
val gen : int -> int list array = <fun>

> gen 10;;
- : int list array =
  [|[1]; [1; 1]; [2; 1]; [1; 2; 1; 1]; [1; 1; 1; 2; 2; 1]; [3; 1; 2; 2; 1; 1];
    [1; 3; 1; 1; 2; 2; 2; 1]; [1; 1; 1; 3; 2; 1; 3; 2; 1; 1];
    [3; 1; 1; 3; 1; 2; 1; 1; 1; 3; 1; 2; 2; 1];
    [1; 3; 2; 1; 1; 3; 1; 1; 1; 2; 3; 1; 1; 3; 1; 1; 2; 2; 1; 1]|]


#load "str.cma";;

let lookandsay =
  Str.global_substitute (Str.regexp "\\(.\\)\\1*")
                        (fun s -> string_of_int (String.length (Str.matched_string s)) ^
                                  Str.matched_group 1 s)

let () =
  let num = ref "1" in
  print_endline !num;
  for i = 1 to 10 do
    num := lookandsay !num;
    print_endline !num;
  done


open Pcre

let lookandsay str =
  let rex = regexp "(.)\\1*" in
  let subs = exec_all ~rex str in
  let ar = Array.map (fun sub -> get_substring sub 0) subs in
  let ar = Array.map (fun s -> String.length s, s.[0]) ar in
  let ar = Array.map (fun (n,c) -> (string_of_int n) ^ (String.make 1 c)) ar in
  let res = String.concat "" (Array.to_list ar) in
  (res)

let () =
  let num = ref(string_of_int 1) in
  for i = 1 to 10 do
    num := lookandsay !num;
    print_endline !num;
  done


(* see http://oeis.org/A005150 *)

let look_and_say s =
let n = String.length s
and buf = Buffer.create 0
and prev = ref s.[0]
and count = ref 0 in
let append () = Buffer.add_char buf (char_of_int (48 + !count));
                Buffer.add_char buf !prev in
String.iter (fun c ->
   if c = !prev then incr count else
   begin
      append ();
      prev := c;
      count := 1
   end
) s;
append ();
Buffer.contents buf;;

(* what about length of successive strings ? *)
let iter f a n =
let rec aux r n v = if n = 0
                    then List.rev(r::v)
                    else aux (f r) (n - 1) (r::v) in
aux a n [];;

let las = iter look_and_say "1";;

(* the first sixty terms *)

List.map (String.length) (las 59);;
(*
   [1; 2; 2; 4; 6; 6; 8; 10; 14; 20; 26; 34; 46; 62; 78; 102; 134; 176; 226;
    302; 408; 528; 678; 904; 1182; 1540; 2012; 2606; 3410; 4462; 5808; 7586;
    9898; 12884; 16774; 21890; 28528; 37158; 48410; 63138; 82350; 107312;
    139984; 182376; 237746; 310036; 403966; 526646; 686646; 894810; 1166642;
    1520986; 1982710; 2584304; 3369156; 4391702; 5724486; 7462860; 9727930;
    12680852]
*)

(* see http://oeis.org/A005341 *)