Prolog-列表成字符串 [英] Prolog - List into String

问题描述

我已经在这里寻找解决方案了，但是什么也没做，所以我决定问一下.

im done of searching here for a solution but nothing so i decided to ask.

因此，我有一个查询，该查询在列表中返回如下内容:

So, i have a query that returns in a list something like this:

List = [6-"read",3-"magazines",3-"music",1-"sport"].

我需要执行转换，这样我才能得到这样的列表:

And i need to perform a transformation so do i can get the list like this:

List = [read,magazines,music,sport]. 
or 
List = ["read","magazines","music","sport"].

为此，我认为我应该先将其传递给字符串以取出数字和-".但是我为此苦苦挣扎.

For that i think i should pass first the to a string to take out the numbers and the '-'. But im struggling with that.

希望有人可以帮助我！谢谢

Hope someone can help me! Thanks

推荐答案

这看起来像是作业，所以我不会为您提供完整的实现.您正在寻找的是规则头中的模式匹配:

This looks like homework, so I will not give you the full implementation. What you are looking for is pattern matching in a rule head:

fst_pair(X, pair(X,Y)).

-运算符只是一个中缀函数符号，因此您可以编写

The - operator is just an infix function symbol such that you could write

fst(X, X-Y).

使用这种模式匹配，可以很容易地在列表上编写一个递归谓词.对于空列表，它必须具有基本大小写，对于列表的首尾必须具有步进大小写:

Using this kind of pattern matching it should be easy to write a recursive predicate over the list. It must have a base case for the empty list and a step case for a head followed by the tail of the list:

fsts_list([], []).
fsts_list([ ... | TailFirsts ], [... | Pairs] ) :- % replace ... by some terms
   % possibly insert some predicates here, depending on what you do above
   fst_lists(TailFirsts, Pairs). 

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