Grabs the stock price (from the Yahoo! finance API) of all passed symbols

finance.ml

open Core.Std
open Yfinance_j

type json = string
type symbol = string
type price = float

let url symbols = 
  "http://finance.yahoo.com/webservice/v1/symbols/"
  ^ (String.concat ~sep:"," symbols)
  ^ "/quote?format=json"

let stock_data symbols =
  let open Http_client.Convenience in
  http_get (url symbols)

let quotes_of_response json =
  let response = Yfinance_j.response_of_string json in
  let quotes = List.map ~f:(fun request -> request.resource.fields) response.list.resources in
  List.map ~f:(fun quote -> (quote.symbol, quote.price)) quotes

let of_string symbol = symbol
let to_string symbol = symbol
let of_float price = price
let to_float price = price

finance.mli

(* abstract types *)
type json
type symbol
type price

(* finance interface *)
val url : symbol list -> json
val stock_data : symbol list -> json
val quotes_of_response : json -> (symbol * price) list

(* helpers to translate from abstract to concrete types *)
val of_string : string -> symbol
val to_string : symbol -> string
val of_float : float -> price
val to_float : price -> float

Makefile

all: atdgen stock_price

stock_price:
        corebuild -pkg core_extended,netclient,yojson,atdgen stock_price.native 

atdgen:
        atdgen -j yfinance.atd
        atdgen -t yfinance.atd

clean:
        rm -f *.native
        rm -rf _build/  
        rm yfinance_*.ml*

stock_price.ml

open Core.Std
open Finance

type symbol = Finance.symbol
type price = Finance.price
type quote = symbol * price

let quotes symbols =
  let open Finance in
  quotes_of_response (stock_data symbols)

let rec display = function
  | [] -> ()
  | (symbol, price) :: tl ->
    printf "%s: %0.2f\n" (Finance.to_string symbol) (Finance.to_float price);
    display tl

exception Symbol_required of string
let remove_first = function
  | [] | [_] -> raise (Symbol_required "You must provide at least one element")
  | _ :: tl -> tl

let () =
  let symbols = remove_first (Array.to_list Sys.argv) in
  display (quotes (List.map ~f:Finance.of_string symbols))

stock_price.mli

(* abstract types *)
type symbol
type price
type quote

(* leaky list interface *)
val remove_first : 'a list -> 'a list

(* stock prices interface *)
val quotes : symbol list -> quote list

(* Output functions *) 
val display : quote list -> unit

yfinance.atd

type response_class = [
    Resource_list <json name="resource-list">
]

type meta = {
    response_type <json name="type"> : response_class;
    start : int;
    count : int;
}

type asset_class = [
    Equity <json name="equity">
    | Money_market <json name="moneymarket">
    | Mutual_fund <json name="mututalfund">
]

type quote = {
    name : string;
    price : float;
    symbol : string;
    ts : int;
    asset_type <json name="type"> : asset_class;
    utctime : string;
    volume : int;
}

type resource = {
    classname : string;
    fields : quote;
}

type result = {
    resource : resource;
}

type results = {
    meta : meta;
    resources : result list;
}

type response = {
    list : results;
}

Rely on ATDGen to generate the schema for the Yahoo! finance JSON types

Factored out an interface

Factored out a finance interface/implementation