render_table.ml

let lengths row =
  List.map row ~f:String.length

let max_width l1 l2 =
  List.map2_exn l1 l2 ~f:Int.max
;;

let widths header rows =
  List.fold rows
    ~init:(lengths header) 
    ~f:(fun acc row ->
      max_width acc (lengths row)
    )
;;

let banner width =
  let banners = List.map width ~f:(fun len -> String.make len '-') in
  "|" ^ String.concat banners ~sep:"+" ^ "|\n"
;;

let line words width = 
  let padded_words = List.map2_exn words width 
    ~f:(fun word width -> word ^ (String.make (width - String.length word) ' '))
  in
  "|" ^ String.concat padded_words ~sep:"|" ^ "|\n"
;;

let render_table header rows =
  let width = widths header rows in
  let banner = banner width in
  let lines = List.map rows
    ~f:(fun words -> line words width)
  in
  String.concat lines ~sep:banner
;;

printf "%s\n" (render_table ["language";"architect";"first release"] [ ["Lisp" ;"John McCarthy" ;"1958"] ;
       ["C"    ;"Dennis Ritchie";"1969"] ;
       ["ML"   ;"Robin Milner"  ;"1973"] ;
       ["OCaml";"Xavier Leroy"  ;"1996"] ;
])
;;