SWI-Prolog:如何从转义字符串中获取 unicode 字符? [英] SWI-Prolog: How to get unicode char from escaped string?

问题描述

我遇到了一个问题，我有一个转义字符串，例如\\u0026"，我需要将其转换为 unicode char '\u0026'.

I have a problem, I've got an escaped string for example "\\u0026" and I need this to transform to unicode char '\u0026'.

像这样的技巧string_concat('\\', S, "\\u0026"), write(S).没有帮助，因为它会删除 \ 不仅是 escape .所以基本上我的问题是，如何从字符串中删除转义字符.

Tricks like string_concat('\\', S, "\\u0026"), write(S). didn't help, because it will remove \ not only the escape . So basically my problem is, how to remove escape chars from the string.

哦，我刚刚注意到，stackoverflow 也可以使用转义 \.

Oh, I've just noticed, that stackoverflow also plays with escape \.

write_canonical/1 给了我\\u0026"，如何将其转换为单个&"字符?

write_canonical/1 gives me "\\u0026", how to transform that into a single '&' char?

推荐答案

在 ISO Prolog 中，char 通常被认为是长度为 1 的原子.原子和字符用单引号括起来，或者不写如果可能的话，报价.以下是一些示例:

In ISO Prolog a char is usually considered an atom of length 1. Atoms and chars are enclosed in single quotes, or written without quotes if possible. Here are some examples:

?- X = abc.       /* an atom, but not a char */
X = abc
?- X = a.         /* an atom and also a char */
X = a
?- X = '\u0061'. 
X = a

\u 符号是特定于 SWI-Prolog 的，在 ISO 中找不到序言.在 SWI-Prolog 中，再次找不到数据类型字符串在 ISO Prolog 中，并始终用双引号括起来.这里有一些例子:

The \u notation is SWI-Prolog specific, and not found in the ISO Prolog. In SWI-Prolog there is a data type string again not found in the ISO Prolog, and always enclosed in double quotes. Here are some examples:

?- X = "abc".    /* a string */
X = "abc"
?- X = "a".      /* again a string */
X = "a"
?- X = "\u0061".
X = "a"

如果手头有长度为 1 的字符串，则可以将其转换为字符通过谓词 atom_string/2.这是一个 SWI-Prolog 特定的谓词，不在 ISO Prolog 中:

If you have a string at hand of length 1, you can convert it to a char via the predicate atom_string/2. This is a SWI-Prolog specific predicate, not in ISO Prolog:

?- atom_string(X, "\u0061").
X = a
?- atom_string(X, "\u0026").
X = &

一些建议.首先开始学习 ISO Prolog 原子谓词，有相当多的.然后学习 SWI-Prolog 原子和字符串谓词.

Some recommendation. Start learning the ISO Prolog atom predicates first, there are quite a number. Then learn the SWI-Prolog atom and string predicates.

您不必学习这么多新的 SWI-Prolog 谓词，因为在 SWI-Prolog 中，大多数 ISO Prolog 谓词也接受字符串.下面是在第一个参数中使用字符串的 ISO Prolog 谓词 atom_codes/2 的示例:

You dont have to learn so many new SWI-Prolog predicates, since in SWI-Prolog most of the ISO Prolog predicates also accept strings. Here is an example of the ISO Prolog predicate atom_codes/2 used with a string in the first argument:

?- atom_codes("\u0061\u0026", L).
L = [97, 38].
?- L = [0'\u0061, 0'\u0026].
L = [97, 38].
?- L = [0x61, 0x26].
L = [97, 38].

P.S: ISO Prolog 中定义了 0' 表示法，它既不是字符、原子或字符串，而是代表整数数据类型.该值是 0' 后给定字符的代码.我将它与 SWI-Prolog \u 符号结合起来.

P.S: The 0' notation is defined in the ISO Prolog, its neither a char, atom or string, but it represents an integer data type. The value is the code of the given char after the 0'. I have combined it with the SWI-Prolog \u notation.

P.P.S:\u 符号中的 0' 符号当然是多余的，在 ISO Prolog 中可以直接使用十六进制符号前缀 0x 表示整数值.

P.P.S: The 0' notation in connection of the \u notation is of course redundant, in ISO Prolog one can directly use the hex notation prefix 0x for integer values.

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