Print a triangle

print_triangle.ml

(* http://www.problemotd.com/problem/party-hat/ *)

open Core.Std;;
open Sequence;;

let print_party_hat height =
  let hat_width line_no =
    2*line_no + 1 in
  let print_char_n char n =
    String.make n char
    |> print_string in
  let line_width = hat_width height in
  let print_party_line n =
    let hat_char_width = hat_width n in
    let half_space_width = (line_width - hat_char_width) / 2 in
    print_char_n ' ' half_space_width;
    print_char_n '*' hat_char_width;
    print_char_n ' ' half_space_width;
    print_newline ()
  in
  iter print_party_line (int_range ~start:0 ~stop:(height - 1))
;;

let () =
  print_party_hat (int_of_string Sys.argv.(1))
;;

(*
$ corebuild -pkg core,sequence print_triangle.byte
$ ./party_hat.byte 4
    *    
   ***   
  *****  
 ******* 
*)