Prolog 应添加哪些DCG规则？

好的，我使用prolog来构建一个简单的xml解析器。我有以下xml文件：

以下是我得到的：

program_state(
     ip(line(7), envt(p1)), 
     contour(name(main), 
         items(item(var(x), val(2)), 
               item(var(y), val(2))), 
     rpdl(system), 
     nested(contour(name(p1), 
             items(item(var(y), val(0)), 
                   item(var(q), val(p2))), 
             rpdl(line(21), envt(main))
               )))).

---

我对XML进行了标记，并将其提供给解析器，结果很好。验证输入：需要引用带有冒号（：）的符号；否则，它们表示

模块名称：模块特定的\u符号

。以下是输入：

?- listing(input).
input([<, program_state, >, <, ip, >, <, line, >, '7', <, /, line, >, <, envt, >, ['p1:1', in, 'main:1'], <, /, envt, >, <, /, ip, >, <, contour, >, <, name, >, 'main:1', <, /, name, >, <, items, >, <, item, >, <, var, >, 'x:int', <, /, var, >, <, val, >, '2', <, /, val, >, <, /, item, >, <, item, >, <, var, >, 'y:int', <, /, var, >, <, val, >, '2', <, /, val, >, <, /, item, >, <, /, items, >, <, rpdl, >, system, <, /, rpdl, >, <, nested, >, <, contour, >, <, name, >, 'p1:1', <, /, name, >, <, items, >, <, item, >, <, var, >, 'y:int', <, /, var, >, <, val, >, '0', <, /, val, >, <, /, item, >, <, item, >, <, var, >, 'q:proc', <, /, var, >, <, val, >, [p2, in, 'main:1'], <, /, val, >, <, /, item, >, <, /, items, >, <, rpdl, >, <, line, >, '21', <, /, line, >, <, envt, >, ['main:1', in, 'root:1'], <, /, envt, >, <, /, rpdl, >, <, /, contour, >, <, /, nested, >, <, /, contour, >, <, /, program_state, >]).

true.

解析器运行的列表：

?- run.
% input.db compiled 0.00 sec, 2,768 bytes
[program_state(ip(line(7),envt([p1:1,in,main:1])),contour(name(main:1),items(item(var(x:int),val(2)),item(var(y:int),val(2))),rpdl(system),nested(contour(name(p1:1),items(item(var(y:int),val(0)),item(var(q:proc),val([p2,in,main:1]))),rpdl(line(21),envt([main:1,in,root:1]))))))]
true 

---

有什么想法吗？我试图添加“elements（E）-->[E]”，但它引发了异常……有趣的是：SWI Prolog感谢您的回答！我实际上添加了以下规则：元素（[X:N]）-->[X'，：'，，N]。元素（[X'in'Y:N]）-->[X，'in'，Y'，：'，N]。元素（[X:N'in'Y:M]）-->[X'，：'，N'，in'，Y'，：'，M]。这样就行了。看起来像是IDE或其他代码隐藏工具的一部分。

program_state(
     ip(line(7), envt(p1)), 
     contour(name(main), 
         items(item(var(x), val(2)), 
               item(var(y), val(2))), 
     rpdl(system), 
     nested(contour(name(p1), 
             items(item(var(y), val(0)), 
                   item(var(q), val(p2))), 
             rpdl(line(21), envt(main))
               )))).

?- listing(input).
input([<, program_state, >, <, ip, >, <, line, >, '7', <, /, line, >, <, envt, >, ['p1:1', in, 'main:1'], <, /, envt, >, <, /, ip, >, <, contour, >, <, name, >, 'main:1', <, /, name, >, <, items, >, <, item, >, <, var, >, 'x:int', <, /, var, >, <, val, >, '2', <, /, val, >, <, /, item, >, <, item, >, <, var, >, 'y:int', <, /, var, >, <, val, >, '2', <, /, val, >, <, /, item, >, <, /, items, >, <, rpdl, >, system, <, /, rpdl, >, <, nested, >, <, contour, >, <, name, >, 'p1:1', <, /, name, >, <, items, >, <, item, >, <, var, >, 'y:int', <, /, var, >, <, val, >, '0', <, /, val, >, <, /, item, >, <, item, >, <, var, >, 'q:proc', <, /, var, >, <, val, >, [p2, in, 'main:1'], <, /, val, >, <, /, item, >, <, /, items, >, <, rpdl, >, <, line, >, '21', <, /, line, >, <, envt, >, ['main:1', in, 'root:1'], <, /, envt, >, <, /, rpdl, >, <, /, contour, >, <, /, nested, >, <, /, contour, >, <, /, program_state, >]).

true.

?- listing(run).
run :-
    consult('input.db'),
    input(A),
    phrase(xml(B), A),
    write(B),
    nl.

true.

?- run.
% input.db compiled 0.00 sec, 2,768 bytes
[program_state(ip(line(7),envt([p1:1,in,main:1])),contour(name(main:1),items(item(var(x:int),val(2)),item(var(y:int),val(2))),rpdl(system),nested(contour(name(p1:1),items(item(var(y:int),val(0)),item(var(q:proc),val([p2,in,main:1]))),rpdl(line(21),envt([main:1,in,root:1]))))))]
true