在 SWI-prolog 中调试 - 未绑定变量
考虑以下 Prolog 代码。它在其输入中编辑特定类型的行，并打印出剩余的行，而不进行任何更改。它使用一个名为 rule 的 DCG，该 DCG 未包含在下面，因为它对问题并不重要。
go:-
prompt(_, ''),
processInput.
processInput:-
read_line_to_codes(current_input, Codes),
processInput(Codes).
processInput(Codes):-
(Codes \= end_of_file
->
(phrase(rule(Part1, Part2), Codes)
->
format('~s - ~s\n', [ Part1, Part2 ])
;
format('~s\n', [ Codes ])),
processInput
;
true).
:- go, halt.
这很好用。但是，假设我将 processInput/1 更改为以下内容，它只是说警告：/home/asfernan/tmp/tmp.pl:28：目标（指令）失败：用户：（走，停止）。
processInput(Codes):-
(Codes \= end_of_file
->
(\+phrase(rule(Part1, Part2), Codes)
->
format('~s\n', [ Codes ]))
;
format('~s - ~s\n', [ Part1, Part2 ]),
processInput
;
true).
如果& phrase(rule(Part1, Part2), Codes) DCG 匹配的其他部分已交换。这显然是一个新手错误，但 go,halt 失败的事实并没有多大帮助。我该怎么做才能使错误消息表明失败是因为 Part1 & Part2 未绑定在 format('~s - ~s\n', [ Part1, Part2 ]) 行中？我能够找到这个错误，因为代码很小，但如果代码很大，我可能无法做到这一点。
Consider the following Prolog code. It edits lines of a particular type in its input and prints out the remaining lines w/o any change. It uses a DCG called rule which isn't included below, since it's not important to the question.
go:-
prompt(_, ''),
processInput.
processInput:-
read_line_to_codes(current_input, Codes),
processInput(Codes).
processInput(Codes):-
(Codes \= end_of_file
->
(phrase(rule(Part1, Part2), Codes)
->
format('~s - ~s\n', [ Part1, Part2 ])
;
format('~s\n', [ Codes ])),
processInput
;
true).
:- go, halt.
This works fine. However, suppose I change processInput/1 to the following, it just says that Warning: /home/asfernan/tmp/tmp.pl:28: Goal (directive) failed: user: (go,halt).
processInput(Codes):-
(Codes \= end_of_file
->
(\+phrase(rule(Part1, Part2), Codes)
->
format('~s\n', [ Codes ]))
;
format('~s - ~s\n', [ Part1, Part2 ]),
processInput
;
true).
The if & else parts of the phrase(rule(Part1, Part2), Codes) DCG match have been exchanged. This is obviously a newbie mistake, but the fact that go, halt failed isn't very helpful. What can I do to make the error message indicate that the failure was because Part1 & Part2 were not bound in the format('~s - ~s\n', [ Part1, Part2 ]) line? I was able to track down this error because the code is small, but I may not have been able to do so had the code been big.
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在 Prolog 中，以下情况是不一样的：
并且
一般情况下，目标
\+ Cond永远不会实例化其变量。所以你必须坚持原来的配方。
如果您有兴趣处理整个
带有 DCG 的文件，请考虑 SWI 的
library(pio)。In Prolog the following is not the same:
and
In general, a goal
\+ Condwill never instantiate its variables. So youhave to stick to the original formulation.
In case you are interested to process entire
files with DCGs, consider SWI's
library(pio).