在 Prolog 中读取字符串(从文件中) [英] Reading a string (from a file) in Prolog

问题描述

我在 Prolog 中编写了一个词法分析器和一个解析器.它将字符串与其 AST 统一起来.这是我正在处理的编译器/解释器项目的一部分.当然，我现在想从文件中读取字符串来解析它.但是，我为此找到的谓词是read，它只读取 Prolog 原子和谓词，就像带有

I have written a lexer and a parser in Prolog. It unifies a string with its AST. This is part for a compiler/interpreter project I am working on. Naturally, I now want to read the string from a file to parse it. However, the predicates I have found for this is read, and it only reads Prolog atoms and predicates, like files with

hello.

我一直在使用 double_quotes 设置，但没有成功.

I have been twiddling with the double_quotes settings, but with no success.

我希望能够读取这样的文件

I want to be able to read a file with something like this

let id = \x.x in id (S (S Z))

然后将此字符串发送到解析谓词.

and then send this string to the parsing predicates.

推荐答案

您可以使用 read_line_to_codes/2 或 read_line_to_codes/3.一个示例程序，它从 stdin 读取单行并将它们打印到 stdout 如下:

You can use read_line_to_codes/2 or read_line_to_codes/3. An example program which reads individual lines from stdin and prints them to stdout is the following:

read_lines([H|T]) :-
  read_line_to_codes(user_input, H), H \= end_of_file, read_lines(T).
read_lines([]).

write_lines([]).
write_lines([H|T]) :-
  writef("%s\n", [H]), write_lines(T).

main :-
  read_lines(X), write_lines(X).

(这使用 writef/2 用于打印.)还有 read_stream_to_codes/2 和 read_stream_to_codes/3，与线条无关.以下代码将所有来自 stdin 的输入一次性打印到 stdout:

(This uses writef/2 for printing.) There are also read_stream_to_codes/2 and read_stream_to_codes/3, which are not concerned with lines. The following code prints all input from stdin in one go to stdout:

main :-
  read_stream_to_codes(user_input, X), writef("%s", [X]).

当然也可以从文件而不是标准输入中读取.有关更多信息，请参阅 readutil 库.

Of course it's also possible to read from a file instead of stdin. For more, see the readutil library.

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