以“原始"./2 格式显示列表 [英] Display a list in its 'raw' ./2 format
问题描述
是否可以以 ./2 格式显示 Prolog 列表,例如
Is it possible to display a Prolog list in its ./2 format, e.g.
对于列表:
| ?- L=[a,b,c].
L = [a,b,c] ?
yes
有没有办法显示:
L = .(a, .(b, .(c, []))).
推荐答案
通常,write_canonical(List)
或 ?- write_term(List, [quoted(true), ignore_ops(true)])
,正如评论中指出的那样.由于 SWI-Prolog 决定做不同的事情,这不是足够好:
Normally, write_canonical(List)
or ?- write_term(List, [quoted(true), ignore_ops(true)])
, as pointed out in the comments. Since SWI-Prolog decided to do things differently, this is not good enough:
?- write_canonical([a]).
[a]
true.
?- write_term([a], [quoted(true), ignore_ops(true)]).
[a]
true.
?- write_term([a], [dotlists(true)]).
.(a,[])
true.
请参阅 关于 write_term/2
的文档,注意选项brace_terms(Bool)
和dotlists(Bool)
.但要注意:如果你正常启动 SWI-Prolog 7,./2
就不再是列表函子了!
See the documentation on write_term/2
, pay attention to the options brace_terms(Bool)
and dotlists(Bool)
. But beware: if you start SWI-Prolog 7 normally, the ./2
is not the list functor any more!
?- L = .(a, []).
ERROR: Type error: `dict' expected, found `a' (an atom) % WHAT?
?- L = '[|]'(a, []).
L = [a].
如果你用 swipl --traditional
开始,一切都会恢复正常,有点:
If you start it with swipl --traditional
, things are back to normal, sort of:
$ swipl --traditional
Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 7.3.4-32-g9311e51)
Copyright (c) 1990-2015 University of Amsterdam, VU Amsterdam
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.
For help, use ?- help(Topic). or ?- apropos(Word).
?- L = .(a, []).
L = [a].
你仍然不能使用 write_canonical(List)
或 write_term(List, [quoted(true), ignore_ops(true)])
.
You still cannot use write_canonical(List)
or write_term(List, [quoted(true), ignore_ops(true)])
.
阅读 SWI-Prolog 文档的链接部分了解详细信息和基本原理.作为建议,如果您决定使用 SWI-Prolog,请坚持使用默认设置的 SWI-Prolog 7,并且仅在需要与另一个 Prolog 通信时才使用 write_term(List, [dotlists(true)])
执行.通常的列表表示法,[a, b, ...]
在大多数常规情况下应该足够好.
Read the linked section of the SWI-Prolog documentation for details and rationale. As an advice, if you decide to use SWI-Prolog stick to SWI-Prolog 7 with the defaults and only use write_term(List, [dotlists(true)])
if you need to communicate with another Prolog implementation. The usual list notation, [a, b, ...]
should be good enough in most conventional situations.
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