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

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

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,"_","_"]

"_" 字面上是字符下划线 "_" 这里，而不是通配符.问题是如何编写谓词 pred(List,List2) 然后将所有 "_" 转换为变量但保持 9 仍然在同一位置?所以如果我输入

"_" 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].

我知道我是否定义了一个谓词

I know if I define a predicate

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

然后通过调用 pred(a,X) 我可以得到类似的结果.但问题是如何让它适应各种输入列表，9 可能在另一个位置，或者列表可能有不同的大小.有人可以帮帮我吗?

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).

交换 '_' 与 "_" 如果您实际上有一个字符串并且没有下划线原子.此外，还有一个 read 谓词可以执行您想要实现的操作，但它需要一个 . 在文件中的列表之后.

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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