使用erlang的动态执行编写DSL

今天看到Erlang 动态执行和erlang动态解释，
实验的代码如下：

-module(dsl).

-compile([export_all]).

broker() ->
     receive
       {buy, Quantity, Ticker} ->
          % 向外部系统下单的具体代码放在这里
          %
          Msg = "Order placed: buying ~p shares of ~p~n",
          io:format(Msg, [Quantity, Ticker]),
          broker();
       {sell, Quantity, Ticker} ->
          % 向外部系统下单的具体代码放在这里
          %
          Msg = "Order placed: selling ~p shares of ~p~n",
          io:format(Msg, [Quantity, Ticker]),
          broker()
     end.

load_biz_rules(Pid, File) ->
     {ok, Bin} = file:read_file(File),
     Rules = string:tokens(erlang:binary_to_list(Bin), "\n"),
     [rule_to_function(Pid, Rule) || Rule <- Rules].

rule_to_function(Pid, Rule) ->
     {ok, Scanned, _} = erl_scan:string(Rule),
     [{_,_,Action},{_,_,Quantity},_,_|Tail] = Scanned,
     [{_,_,Ticker},_,_,_,{_,_,Operator},_,{_,_,Limit}] = Tail,
     to_function(Pid, Action, Quantity, Ticker, Operator, Limit).

to_function(Pid, Action, Quantity, Ticker, Operator, Limit) ->
     fun(Ticker_, Price) ->
        if
          Ticker =:= Ticker_ andalso
          ( ( Price < Limit andalso Operator =:= less ) orelse 
            ( Price > Limit andalso Operator =:= greater ) ) ->
              Pid ! {Action, Quantity, Ticker}; % place an order 
          true ->
              erlang:display("no rule applied")
        end
     end.

apply_biz_rules(Functions, MarketData) ->
        lists:map(fun({Ticker,Price}) ->
                lists:map(fun(Function) ->
                                 Function(Ticker, Price)
                           end, Functions)
                 end, MarketData),
	ok.

用到的biz_rules.txt内容如下：

引用

buy 9000 shares of GOOG when price is less than 500
sell 400 shares of MSFT when price is greater than 30
buy 7000 shares of AAPL when price is less than 160

执行的结果如下：

[root@dev-emp-com work]# erl
Erlang R14B (erts-5.8.1) [source] [64-bit] [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.8.1  (abort with ^G)
1> Pid = spawn(fun() -> dsl:broker() end). 
<0.34.0>
2> 
2> Functions = dsl:load_biz_rules(Pid, "biz_rules.txt").
[#Fun<dsl.0.70661670>,#Fun<dsl.0.70661670>,
 #Fun<dsl.0.70661670>]
3> MarketData = [{'GOOG', 498}, {'MSFT', 30}, {'AAPL', 158}].
[{'GOOG',498},{'MSFT',30},{'AAPL',158}]
4> dsl:apply_biz_rules(Functions, MarketData).
"no rule applied"
"no rule applied"
"no rule applied"
"no rule applied"
"no rule applied"
"no rule applied"
"no rule applied"
Order placed: buying 9000 shares of 'GOOG'
ok
Order placed: buying 7000 shares of 'AAPL'
5>