为什么此规则不使用第一个字符[Prolog CFG]？

Question

我正在尝试编写一个用于包装元素的规则，但是当输入递归规则时，第一个元素仍被包括在内，也许我对语法的理解不正确，但是逗号不应该转到下一个元素？

% [First] should be consumed (note: charcode 194 is for the backtick character)
backticks(L) --> [First], {char_code(First,194), writeln(["first was backtick",First])}, nobackticks(L), {writeln(["identifier",L])}.
nobackticks([]) --> [Last], {char_code(Last,194),writeln(["last is backtick",Last])}.
nobackticks([X|Xs]) --> [X], nobackticks(Xs), {writeln(["checking backticks",X,Xs])}.
%run recursively until it finds the last backtick

测试

:- string_chars("´backticks´",Text), phrase(backticks(X),Text,[]), writeln(X).

输出：

[first was backtick,´]
[last is backtick,´]
[checking backticks,s,[]]
[checking backticks,k,[s]]
[checking backticks,c,[k,s]]
[checking backticks,i,[c,k,s]]
[checking backticks,t,[i,c,k,s]]
[checking backticks,k,[t,i,c,k,s]]
[checking backticks,c,[k,t,i,c,k,s]]
[checking backticks,a,[c,k,t,i,c,k,s]]
[checking backticks,b,[a,c,k,t,i,c,k,s]]
[checking backticks,´,[b,a,c,k,t,i,c,k,s]]
[identifier,[´,b,a,c,k,t,i,c,k,s]]

预期输出：

[identifier,[b,a,c,k,t,i,c,k,s]]

最后规则不成功

Answer 1

如果您运行?- char_code(´,C).，您会得到C=180（至少在SWISH中）。因此，您需要在代码中将194更改为180，您将获得所需的输出：

[first was backtick, ´]
[last is backtick, ´]
[checking backticks, s, []]
[checking backticks, k, [s]]
[checking backticks, c, [k, s]]
[checking backticks, i, [c, k, s]]
[checking backticks, t, [i, c, k, s]]
[checking backticks, k, [t, i, c, k, s]]
[checking backticks, c, [k, t, i, c, k, s]]
[checking backticks, a, [c, k, t, i, c, k, s]]
[checking backticks, b, [a, c, k, t, i, c, k, s]]
[identifier, [b, a, c, k, t, i, c, k, s]]
[b, a, c, k, t, i, c, k, s]
true
false