将字符串转换为序言中的列表 [英] convert string to list in prolog

问题描述

我是 Prolog 新手，我一直在将字符串解析为列表.我有一个

I am a Prolog newbie and am stuck at parsing a string to a list. I have a string of the form

1..2...3..4

我想把它转换成一个看起来像的列表

I wish to convert it into a list which looks like

[1, _, _, 2, _, _, _, 3, _, _, 4]

我怎样才能实现这个功能?

How can I achieve this functionality?

推荐答案

另一种解决方案是使用 DCG.代码很简单:

Another solution is to use DCG's. The code is straightforward:

digit(N) -->
    [ D ], { member(D, "0123456789"), number_codes(N, [D]) }.

dot(_) --> ".".

token(T) --> digit(T).
token(T) --> dot(T).

tokens([T|Ts]) --> token(T), tokens(Ts).
tokens([]) --> "".

parse_codes(In, Out):-
    phrase(tokens(Out), In, "").

parse_atom(In, Out):-
    atom_codes(In, Codes),
    parse_codes(Codes, Out).

使用字符串"(实际上只是代码列表)在 SWI-Prolog 上进行测试:

Testing on SWI-Prolog with "string" (which is actually just a list of codes):

?- parse_codes("1..24.4", Out).
Out = [1, _G992, _G995, 2, 4, _G1070, 4] .

还有一个原子(在使用相同谓词之前只是转换为代码):

And with an atom (which is just converted to codes before using the same predicate):

?- parse_atom('1..22.4', Out).
Out = [1, _G971, _G974, 2, 2, _G1049, 4] .

SWI-Prolog 以更高级的符号打印匿名变量 (_)，否则它应该与您需要的结果相同.

SWI-Prolog prints anonymous variables (_) in a bit fancier notation but otherwise it should be the same result you need.

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