我想出了如何使用螺纹钢。我试图使用jsx（jiffy在Windows上无法正常工作）来解析我使用openexchangerates.org API获得的json，但我甚至无法弄清楚如何正确使用Erlang＆＃ 39;广泛的二进制功能，以便解压获得的JSON元组。使用以下代码片段，我设法得到一个包含我需要的所有数据的元组：
-module(currency).
-export([start/0]).
start() ->
URL = "http://openexchangerates.org",
Endpoint = "/api/latest.json?app_id=<myprivateid>",
X = string:concat(URL, Endpoint),
% io:format("~p~n",[X]).
inets:start(),
{ok, Req} = httpc:request(X),
Req.
以下是获得的回复：
9> currency:start().
{{"HTTP/1.1",200,"OK"},
[{"cache-control","public"},
{"connection","close"},
{"date","Fri, 15 Aug 2014 01:28:06 GMT"},
{"etag","\"d9ad180d4af1caaedab6e622ec0a8a70\""},
{"server","Apache"},
{"content-length","4370"},
{"content-type","application/json; charset=utf-8"},
{"last-modified","Fri, 15 Aug 2014 01:00:56 GMT"},
{"access-control-allow-origin","*"}],
"{\n \"disclaimer\": \"Exchange rates are provided for informational purposes only, and do not constitute financial advice of any kind. Although every attempt is made to ensure quality, NO guarantees are given whatsoever of accuracy, validity, availability, or fitness for any purpose - please use at your own risk. All usage is subject to your acceptance of the Terms and Conditions of Service, available at: https://openexchangerates.org/terms/\",\n \"license\": \"Data sourced from various providers with public-facing APIs; copyright may apply; resale is prohibited; no warranties given of any kind. Bitcoin data provided by http://coindesk.com. All usage is subject to your acceptance of the License Agreement available at: https://openexchangerates.org/license/\",\n \"timestamp\": 1408064456,\n \"base\": \"USD\",\n \"rates\": {\n \"AED\": 3.673128,\n \"AFN\": 56.479925,\n \"ALL\": 104.147599,\n \"AMD\": 413.859001,\n \"ANG\": 1.789,\n \"AOA\": 97.913074,\n \"ARS\": 8.274908,\n \"AUD\": 1.073302,\n \"AWG\": 1.79005,\n \"AZN\": 0.783933,\n \"BAM\": 1.46437,\n \"BBD\": 2,\n \"BDT\": 77.478631,\n \"BGN\": 1.464338,\n \"BHD\": 0.377041,\n \"BIF\": 1546.956667,\n \"BMD\": 1,\n \"BND\": 1.247024,\n \"BOB\": 6.91391,\n \"BRL\": 2.269422,\n \"BSD\": 1,\n \"BTC\": 0.0019571961,\n \"BTN\": 60.843812,\n \"BWP\": 8.833083,\n \"BYR\": 10385.016667,\n \"BZD\": 1.99597,\n \"CAD\": 1.0906,\n \"CDF\": 924.311667,\n \"CHF\": 0.906799,\n \"CLF\": 0.02399,\n \"CLP\": 577.521099,\n \"CNY\": 6.153677,\n \"COP\": 1880.690016,\n \"CRC\": 540.082202,\n \"CUP\": 1.000688,\n \"CVE\": 82.102201,\n \"CZK\": 20.81766,\n \"DJF\": 178.76812,\n \"DKK\": 5.579046,\n \"DOP\": 43.43789,\n \"DZD\": 79.8973,\n \"EEK\": 11.70595,\n \"EGP\": 7.151305,\n \"ERN\": 15.062575,\n \"ETB\": 19.83205,\n \"EUR\": 0.748385,\n \"FJD\": 1.85028,\n \"FKP\": 0.599315,\n \"GBP\": 0.599315,\n \"GEL\": 1.74167,\n \"GGP\": 0.599315,\n \"GHS\": 3.735499,\n \"GIP\": 0.599315,\n \"GMD\": 39.73668,\n \"GNF\": 6995.309935,\n \"GTQ\": 7.839405,\n \"GYD\": 205.351249,\n \"HKD\": 7.750863,\n \"HNL\": 21.04854,\n \"HRK\": 5.708371,\n \"HTG\": 44.66625,\n \"HUF\": 233.847801,\n \"IDR\": 11682.083333,\n \"ILS\": 3.471749,\n \"IMP\": 0.599315,\n \"INR\": 60.81923,\n \"IQD\": 1178.211753,\n \"IRR\": 26354,\n \"ISK\": 115.976,\n \"JEP\": 0.599315,\n \"JMD\": 112.604801,\n \"JOD\": 0.707578,\n \"JPY\": 102.501401,\n \"KES\": 88.106539,\n \"KGS\": 51.96,\n \"KHR\": 4056.578416,\n \"KMF\": 368.149,\n \"KPW\": 900,\n \"KRW\": 1021.166657,\n \"KWD\": 0.283537,\n \"KYD\": 0.826373,\n \"KZT\": 182.076001,\n \"LAK\": 8049.834935,\n \"LBP\": 1509.068333,\n \"LKR\": 130.184301,\n \"LRD\": 91.49085,\n \"LSL\": 10.56165,\n \"LTL\": 2.583284,\n \"LVL\": 0.521303,\n \"LYD\": 1.244127,\n \"MAD\": 8.372529,\n \"MDL\": 13.7178,\n \"MGA\": 2495.605,\n \"MKD\": 45.99967,\n \"MMK\": 972.1784,\n \"MNT\": 1884.666667,\n \"MOP\": 7.986251,\n \"MRO\": 292.0081,\n \"MTL\": 0.683602,\n \"MUR\": 30.61708,\n \"MVR\": 15.37833,\n \"MWK\": 392.9201,\n \"MXN\": 13.07888,\n \"MYR\": 3.175156,\n \"MZN\": 30.3522,\n \"NAD\": 10.56145,\n \"NGN\": 162.303701,\n \"NIO\": 26.07651,\n \"NOK\": 6.157432,\n \"NPR\": 97.66846,\n \"NZD\": 1.179688,\n \"OMR\": 0.38501,\n \"PAB\": 1,\n \"PEN\": 2.795018,\n \"PGK\": 2.464545,\n \"PHP\": 43.66429,\n \"PKR\": 99.5662,\n \"PLN\": 3.126223,\n \"PYG\": 4272.421673,\n \"QAR\": 3.641137,\n \"RON\": 3.320192,\n \"RSD\": 87.82784,\n \"RUB\": 36.00216,\n \"RWF\": 690.269,\n \"SAR\": 3.750523,\n \"SBD\": 7.269337,\n \"SCR\": 12.40801,\n \"SDG\": 5.699103,\n \"SEK\": 6.86018,\n \"SGD\": 1.246263,\n \"SHP\": 0.599315,\n \"SLL\": 4372.166667,\n \"SOS\": 841.5678,\n \"SRD\": 3.275,\n \"STD\": 18316.816667,\n \"SVC\": 8.745567,\n \"SYP\": 150.751249,\n \"SZL\": 10.56279,\n \"THB\": 31.86192,\n \"TJS\": 4.9856,\n \"TMT\": 2.8501,\n \"TND\": 1.719658,\n \"TOP\": 1.8861,\n \"TRY\": 2.15338,\n \"TTD\": 6.343484,\n \"TWD\": 30.00481,\n \"TZS\": 1661.865,\n \"UAH\": 13.02466,\n \"UGX\": 2614.28,\n \"USD\": 1,\n \"UYU\": 23.70693,\n \"UZS\": 2337.106637,\n \"VEF\": 6.295009,\n \"VND\": 21191.15,\n \"VUV\": 94.6,\n \"WST\": 2.301222,\n \"XAF\": 491.286739,\n \"XAG\": 0.05031657,\n \"XAU\": 0.00076203,\n \"XCD\": 2.70154,\n \"XDR\": 0.654135,\n \"XOF\": 491.394602,\n \"XPF\": 89.414091,\n \"YER\": 214.985901,\n \"ZAR\": 10.55678,\n \"ZMK\": 5253.075255,\n \"ZMW\": 6.169833,\n \"ZWL\": 322.355006\n }\n}"}
我不明白为什么这段代码无效：
X = "Arthur".
B = <<X>>.
JSX允许大量的解析功能，但只有当我有一个二进制作为我的JSON表示时，我从货币API获得的这个JSON是元组中的一个字符串......我就是这样的有点失去了从哪里开始研究。使用模式匹配解包元组据说非常简单（我已经完成了一些Prolog编程，我可以看到erlang有类似的行为）但是还有另一种更好的Erlang方法来获取＆＃34; rate＆ ＃34;作为回应我收到的JSON的一部分？
谢谢！我正在开发一个很酷的网络应用程序来学习erlang，这是一个很好的第一步。我有三本Erlang书籍，我正在努力阅读它们，但问题是我希望尽可能早地接触实际的曝光。我喜欢这种语言，但我想尽快获得坚实的基础。
谢谢！
答案 0 :(得分：0)
我发现了我的问题。
首先，我没想到简单地计算元组中有多少元素是多么简单。话虽这么说，我意识到只有三个。
所以我需要的是
{A,B,C} = Req.
之后，我只想查看最后一个（C，JSON有效负载），这是一个字符串。 我通过另一个来源发现了（不要忽视你告诉我的，凯！）你需要使用列表函数，因为字符串和ASCII范围内的整数列表（我认为），在本例中为list_to_binary。
一旦我使用了这一行：
D = list_to_binary(C)，随后
E = jsx:decode(D)，我得到了这个输出：
[{<<"disclaimer">>,
<<"Exchange rates are provided for infor
attempt is made to ensure quality, NO gua
se - please use at your own risk. All usag
s://openexchangerates.org/terms/">>},
{<<"license">>,
<<"Data sourced from various providers w
any kind. Bitcoin data provided by http://
t: https://openexchangerates.org/license/"
{<<"timestamp">>,1408068012},
{<<"base">>,<<"USD">>},
{<<"rates">>,
[{<<"AED">>,3.673128},
{<<"AFN">>,56.479925},
{<<"ALL">>,104.1526},
{<<"AMD">>,413.859001},
{<<"ANG">>,1.789},
{<<"AOA">>,97.913949},
{<<"ARS">>,8.274608},
{<<"AUD">>,1.073236},
{<<"AWG">>,1.79005},
{<<"AZN">>,0.783933},
{<<"BAM">>,1.46437},
{<<"BBD">>,2},
{<<"BDT">>,77.478631},
{<<"BGN">>,1.464358},
{<<"BHD">>,0.377041},
{<<"BIF">>,1546.956667},
{<<"BMD">>,1},
{<<"BND">>,1.246774},
{<<"BOB">>,6.91391},
{<<"BRL">>,2.269462},
{<<"BSD">>,1},
{<<"BTC">>,0.0019393375},
{<<"BTN">>,60.843812},
{<<"BWP">>,8.833083},
{<<"BYR">>,10385.016667},
{<<"BZD">>,1.99597},
{<<"CAD">>,1.090486},
{<<"CDF">>,924.311667},
{<<"CHF">>,0.906833},
{<<"CLF">>,0.02399},
{<<"CLP">>,577.521099},
{<<"CNY">>,6.151637},
{<<"COP">>,1880.690016},
{<<"CRC">>,540.082202},
{<<"CUP">>,1.000688},
{<<"CVE">>,82.049699},
{<<"CZK">>,20.818},
{<<"DJF">>,179.084119},
{<<"DKK">>,5.579049},
{<<"DOP">>,43.43789},
{<<"DZD">>,79.8641},
{<<"EEK">>,11.7064},
{<<"EGP">>,7.150475},
{<<"ERN">>,15.062575},
{<<"ETB">>,19.83205},
{<<"EUR">>,0.748419},
{<<"FJD">>,1.850441},
{<<"FKP">>,0.599402},
{<<"GBP">>,0.599402},
{<<"GEL">>,1.74167},
{<<"GGP">>,0.599402},
{<<"GHS">>,3.735499},
{<<"GIP">>,0.599402},
{<<"GMD">>,39.73668},
{<<"GNF">>,6995.309935},
{<<"GTQ">>,7.839405},
{<<"GYD">>,205.351249},
{<<"HKD">>,7.750754},
{<<"HNL">>,21.04854},
{<<"HRK">>,5.708511},
{<<"HTG">>,44.66625},
{<<"HUF">>,233.8448},
{<<"IDR">>,11685.75},
{<<"ILS">>,3.471469},
{<<"IMP">>,0.599402},
{<<"INR">>,60.82523},
{<<"IQD">>,1178.211753},
{<<"IRR">>,26355.666667},
{<<"ISK">>,115.96},
{<<"JEP">>,0.599402},
{<<"JMD">>,112.604801},
{<<"JOD">>,0.707778},
{<<"JPY">>,102.495401},
{<<"KES">>,88.107639},
{<<"KGS">>,51.991},
{<<"KHR">>,4056.578416},
{<<"KMF">>,368.142141},
{<<"KPW">>,900},
{<<"KRW">>,1021.353328},
{<<"KWD">>,0.283537},
{<<"KYD">>,0.826373},
{<<"KZT">>,182.076001},
{<<"LAK">>,8049.834935},
{<<"LBP">>,1509.068333},
{<<"LKR">>,130.184301},
{<<"LRD">>,91.49085},
{<<"LSL">>,10.56165},
{<<"LTL">>,2.583364},
{<<"LVL">>,0.521328},
{<<"LYD">>,1.244147},
{<<"MAD">>,8.372619},
{<<"MDL">>,13.7178},
{<<"MGA">>,2495.605},
{<<"MKD">>,46.00037},
{<<"MMK">>,972.1784},
{<<"MNT">>,1885},
{<<"MOP">>,7.986291},
{<<"MRO">>,292.0081},
{<<"MTL">>,0.683738},
{<<"MUR">>,30.61748},
{<<"MVR">>,15.37833},
{<<"MWK">>,392.9201},
{<<"MXN">>,13.07883},
{<<"MYR">>,3.175406},
{<<"MZN">>,30.3272},
{<<"NAD">>,10.56145},
{<<"NGN">>,162.303701},
{<<"NIO">>,26.07651},
{<<"NOK">>,6.156902},
{<<"NPR">>,97.66846},
{<<"NZD">>,1.179692},
{<<"OMR">>,0.38501},
{<<"PAB">>,1},
{<<"PEN">>,2.795018},
{<<"PGK">>,2.464545},
{<<"PHP">>,43.68439},
{<<"PKR">>,99.5642},
{<<"PLN">>,3.126203},
{<<"PYG">>,4272.421673},
{<<"QAR">>,3.641297},
{<<"RON">>,3.319212},
{<<"RSD">>,87.8205},
{<<"RUB">>,36.00206},
{<<"RWF">>,690.088},
{<<"SAR">>,3.750583},
{<<"SBD">>,7.258136},
{<<"SCR">>,12.40829},
{<<"SDG">>,5.697837},
{<<"SEK">>,6.857347},
{<<"SGD">>,1.246447},
{<<"SHP">>,0.599402},
{<<"SLL">>,4360},
{<<"SOS">>,841.5678},
{<<"SRD">>,3.275},
{<<"STD">>,18322.733333},
{<<"SVC">>,8.745567},
{<<"SYP">>,150.793749},
{<<"SZL">>,10.56279},
{<<"THB">>,31.87122},
{<<"TJS">>,4.985575},
{<<"TMT">>,2.8501},
{<<"TND">>,1.719698},
{<<"TOP">>,1.889033},
{<<"TRY">>,2.15342},
{<<"TTD">>,6.343484},
{<<"TWD">>,29.99281},
{<<"TZS">>,1661.865},
{<<"UAH">>,13.02466},
{<<"UGX">>,2614.28},
{<<"USD">>,1},
{<<"UYU">>,23.70693},
{<<"UZS">>,2337.773304},
{<<"VEF">>,6.295009},
{<<"VND">>,21191.15},
{<<"VUV">>,94.4875},
{<<"WST">>,2.301222},
{<<"XAF">>,491.283058},
{<<"XAG">>,0.05031404},
{<<"XAU">>,7.6211e-4},
{<<"XCD">>,2.70154},
{<<"XDR">>,0.654135},
{<<"XOF">>,491.394602},
{<<"XPF">>,89.416091},
{<<"YER">>,214.985901},
{<<"ZAR">>,10.55649},
{<<"ZMK">>,5252.024745},
{<<"ZMW">>,6.169833},
{<<"ZWL">>,322.355006}]}]
ok
所以这更接近我想要的，但我如何轻松提取特定货币？例如，像ZWL一样。
答案 1 :(得分：0)
get_currencies() ->
URL = "http://openexchangerates.org",
Endpoint = "/api/latest.json?app_id=<myprivateid>",
X = string:concat(URL, Endpoint),
% io:format("~p~n",[X]).
inets:start(),
{ok, {_,_,R}} = httpc:request(X),
E = jsx:decode(lists_to_binary(R)),
Base = proplists:get_value(<<"base">>,E),
Sec = proplists:get_value(<<"timestamp">>,E),
{Days,Time} = calendar:seconds_to_daystime(Sec),
Date = calendar:gregorian_days_to_date(Days+719528),
Currencies = proplists:get_value(<<"rates">>,E),
fun(C) -> V = proplists:get_value(C,Currencies),
{change,Date,Time,Base,C,V}
end.
以及代码中的某处：
GC = get_currencies(), %% you can store GC in an ets, a server state...
%% but don't forget to refresh it :o)
稍后再使用
{change,D,T,B,C,V} = GC(<<"ZWL">>),
%% should return {change,{2014,8,15},{2,0,12},<<"USD">>,<<"ZWL">>,322.355006}
<强> [编辑]
当我使用外部应用程序，如jsx（使用钢筋本身）时，我也使用rebar及其依赖机制来创建我自己的应用程序，在我看来，这是最方便的方法。 （在其他情况下，我也使用钢筋：o）
然后我使用OTP行为（application，supervisor，gen_server ...）构建我的应用程序。编写的模块很多，但有些模块非常简短（应用程序和管理程序），它们有助于应用程序结构（如果您不熟悉，请参阅What is OTP。）
在你的情况下，我的第一个想法是让一个gen服务器在它的状态下构建和存储GC匿名函数，每次它获得诸如update_currencies的强制转换消息，并在每次提供答案时获取一条呼叫消息，例如{get_change,Cur}（如果未定义或过时，可能会刷新GC。）
您还必须决定错误的管理位置 - 它可能无处可去：如果gen_server没有做任何其他事情，只能回答此货币查询：如果出现错误，它将崩溃并由其主管重新启动 - 因为这段代码与外界有很多接口，所以会遇到很多失败（没有互联网访问，网站的答案结构改变，用户的不良货币请求......）