某課題のOCaml実装

car.ml

open Core.Std;;

type car_query =
  | And  of car_query * car_query
  | Or   of car_query * car_query
  | Term of string * string

let cons_exn arg =
  let cons_term_exn item =
    match String.split item '=' with
    | tag :: param :: [] -> Term (tag, param)
    | _ -> invalid_arg "format is 'tag=param'!"
  in
  let rec loop prev = function
    | [] -> prev
    | "or"  :: r :: tl -> loop (Or  (prev, cons_term_exn r)) tl
    | "and" :: r :: tl -> loop (And (prev, cons_term_exn r)) tl
    | _ :: _ ->
      let () = Printf.printf
          "error:Maybe you mistyped the number of arg, I'll return a result so far..."
      in
      prev
  in
  match arg with
  | [] -> invalid_arg "there is no argment"
  | hd :: tl -> loop (cons_term_exn hd) tl

let make_table size record_list =
  let table = String.Table.create () ~size:size in
  List.iter record_list (fun (key, data) -> Hashtbl.set table ~key ~data);
  table

let tag_to_idx = make_table 7 [("buying", 0); ("maint", 1); ("doors", 2); ("persons", 3); ("luggage", 4); ("safety", 5); ("eval", 6)]

let match_query_exn query record =
  let rec loop = function
    | And (st, nd) -> loop st && loop nd
    | Or  (st, nd) -> loop st || loop nd
    | Term (tag, param) ->
      let idx = Hashtbl.find_exn tag_to_idx tag in
      (List.nth_exn record idx) = param
  in
  loop query

let () =
  let csv = In_channel.create "car.csv" in
  let (_ :: query_src) = Array.to_list Sys.argv in
  let rate_table = make_table 4 [("unacc", 0); ("acc", 0); ("good", 0); ("vgood", 0)] in
  let delim = String.split ~on:',' in
  let eval = match_query_exn (cons_exn query_src) in
  let update record = Hashtbl.change rate_table (List.nth_exn record 6)
      (function Some count -> Some (count + 1) | None -> Some 0)
  in
  let update_if_match record = if eval record then update record in
  In_channel.iter_lines csv (fun line -> delim line |> update_if_match);
  Hashtbl.iter rate_table (fun ~key ~data -> Printf.printf "%s = %d, " key data);