Prolog-如何从输入文件的给定列表中制作变量列表? [英] Prolog - How to make a variable list out of a given list from input file?

问题描述

我有一个输入谓词，它将文件作为列表读取:input(Filename，List).然后，该列表将采用

I have a input predicate will read the file as a list: input(Filename,List). The list then will be in the format of

["_","_","_",9,"_","_"]

"_"此处实际上是下划线"_"的字符，而不是通配符.问题是如何编写谓词pred(List，List2)，然后将所有"_"转换为变量，但将9保持在同一位置?因此，如果我输入

"_" is literally the character underscore "_" here, not a wild card. The question is how can I write a predicate pred(List,List2) then transform all the "_" into variables but keep 9 still at the same position? So If I type in

input(Filename,List),pred(List,X).

我会得到类似的东西

X = [_G1426, _G1429, _G1432, 9, _G1438, _G1441].

我知道我是否定义谓词

pred(a,[_,_,_,9,_,_]).

然后通过调用pred(a,X)我可以得到类似的结果.但是问题是如何使其适应所有类型的输入列表，9可能在另一个位置，或者列表的大小可能不同.有人可以帮我吗?

Then by calling pred(a,X) I can have the similar result. But the thing is how to make it adaptive to all kinds of input lists, 9 might be at a another position or the list might be of different size. Can somebody help me?

推荐答案

to_var_list([],[]).
to_var_list([A|R1],[B|R2]):-
     (A = '_' ->
      true;
      A = B),
    to_var_list(R1,R2).

如果您实际上只有一个字符串而不加下划线原子，则将'_'与"_"交换. 另外，有一个read谓词可以实现您想要实现的功能，但是在文件中的列表后面需要一个..

Exchange '_' with "_" if you actually have one character strings and not underscore atoms. Also, there is a read predicate that does something like you want to achieve, but it expects a . after your lists in the file.

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