不知道为什么与 List.iter 一起使用时我会得到未绑定的值

Question

我正在为我的 OCaml 项目编写测试代码，当使用下面的代码时，它工作正常。

open Printf
open Ip2location

(* query IP2Location BIN datababase *)
let meta = Database.open_db "./IP2LOCATION-LITE-DB1.IPV6.BIN";;

let ip = "2a02:3037:0400:6fa2:459c:84b6:967d:69e0";;
let res = Database.query meta ip;;

printf "country_short: %s\n" res.country_short;;
printf "country_long: %s\n" res.country_long;;
printf "region: %s\n" res.region;;
printf "city: %s\n" res.city;;
printf "isp: %s\n" res.isp;;
printf "latitude: %f\n" res.latitude;;
printf "longitude: %f\n" res.longitude;;
printf "domain: %s\n" res.domain;;
printf "zip_code: %s\n" res.zip_code;;
printf "time_zone: %s\n" res.time_zone;;
printf "net_speed: %s\n" res.net_speed;;
printf "idd_code: %s\n" res.idd_code;;
printf "area_code: %s\n" res.area_code;;
printf "weather_station_code: %s\n" res.weather_station_code;;
printf "weather_station_name: %s\n" res.weather_station_name;;
printf "mcc: %s\n" res.mcc;;
printf "mnc: %s\n" res.mnc;;
printf "mobile_brand: %s\n" res.mobile_brand;;
printf "elevation: %f\n" res.elevation;;
printf "usage_type: %s\n" res.usage_type;;
printf "address_type: %s\n" res.address_type;;
printf "category: %s\n" res.category;;
printf "district: %s\n" res.district;;
printf "asn: %s\n" res.asn;;
printf "as: %s\n" res.asys;;

Database.close_db meta;;

然后，我修改了代码来查询 IP 地址列表，如下所示：

open Printf
open Ip2location

(* query IP2Location BIN datababase *)
let meta = Database.open_db "./IP2LOCATION-LITE-DB1.IPV6.BIN";;

let mylist = ["0.0.0.0"; "8.3.34.0"; "8.8.8.8"; "3.91.171.8"; "37.252.228.50"; "64.94.62.0"; "197.85.191.64"; "255.255.255.254"; "255.255.255.255"; "179.125.12.0"; "::"; "2001::"; "2001:0:4136:e378:8000:63bf:f7f7:f7f7"; "2001:0000:4136:e378:8000:63bf:f7fc:ddff"; "2002::"; "2002:808:808::"; "2002:0803:2200::0803:2200"; "2600:1F18:45B0:5B00:0000:0000:0000:0000"; "::FFFF:FFFF"; "::FFFF:3.91.171.8"; "::FFFF:8.3.34.0"; "::FFFF:64.94.62.0"; "::FFFF:C555:BF40"; "ffff:ffff:ffff:ffff:FFFF:FFFF:FFFF:FFFE"; "FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF"; "0:0:0:0:0:ffff:b37d:0c00"; "0.0.0.256"; "0.0.0"; "1"; "A"];;

let getloc ip =
    let res = Database.query meta ip in
    printf "country_short: %s\n" res.country_short;;
    printf "country_long: %s\n" res.country_long;;
    printf "region: %s\n" res.region;;
    printf "city: %s\n" res.city;;
    printf "isp: %s\n" res.isp;;
    printf "latitude: %f\n" res.latitude;;
    printf "longitude: %f\n" res.longitude;;
    printf "domain: %s\n" res.domain;;
    printf "zip_code: %s\n" res.zip_code;;
    printf "time_zone: %s\n" res.time_zone;;
    printf "net_speed: %s\n" res.net_speed;;
    printf "idd_code: %s\n" res.idd_code;;
    printf "area_code: %s\n" res.area_code;;
    printf "weather_station_code: %s\n" res.weather_station_code;;
    printf "weather_station_name: %s\n" res.weather_station_name;;
    printf "mcc: %s\n" res.mcc;;
    printf "mnc: %s\n" res.mnc;;
    printf "mobile_brand: %s\n" res.mobile_brand;;
    printf "elevation: %f\n" res.elevation;;
    printf "usage_type: %s\n" res.usage_type;;
    printf "address_type: %s\n" res.address_type;;
    printf "category: %s\n" res.category;;
    printf "district: %s\n" res.district;;
    printf "asn: %s\n" res.asn;;
    printf "as: %s\n" res.asys

List.iter getloc mylist;;

Database.close_db meta;;

当我运行

dune test

时，我得到以下信息：

File "test/ip2locationtest.ml", line 12, characters 29-32:
12 |    printf "country_long: %s\n" res.country_long;;
                                    ^^^
Error: Unbound value res
Hint: Did you mean ref?

我是 OCaml 的新手，所以我不确定我错过了什么。如果有人指出我做错了什么，我将不胜感激。

Answer 1

双分号

;;

用于在与口译员交谈时标记表达式的结束。因此，您的

let res = ...

以第一个双分号结束。之后

res

不再被定义。

您不应该在代码中使用双分号。这只是与口译员交谈的一种方式。如果您将双分号更改为单分号，效果会更好。