如何检查变量是否包含纯 TeX 中的单词？

Question

我有一个包含一长串关键字的变量，例如：

\keywords{computers, business, biology, fine art, literature, zoology}

我需要创建一个 if-then 语句来检查特定关键字是否存在，例如：

IF "zoology" IN keywords
THEN
    TRUE
ELSE
    FALSE

如何在纯 TeX 中检查变量是否包含特定关键字？

• 我可以更改的格式\keywords，例如\keywords{computers biology fine_art}，如果这样更容易实现的话。

Answer 1

以下示例使用包kvsetkeys来获取以逗号分隔条目的列表的解析器：

\input kvsetkeys.sty % parser for comma separated lists
\input ltxcmds.sty % helper macros

\catcode`\@=11 % \makeatletter
\newif\ifkey@found

% \testkeywordinlist{keyword}{keyword list}{true}{false}
\def\testkeywordinlist#1#2{%
  \edef\key@word{#1}%
  \edef\key@list{#2}%
  \key@foundfalse
  \expandafter\comma@parse\expandafter{\key@list}{%
    \ifx\comma@entry\key@word
      \key@foundtrue
      \comma@break
    \fi
    \ltx@gobble
  }%
  \ifkey@found
    \expandafter\ltx@firstoftwo
  \else
    \expandafter\ltx@secondoftwo
  \fi
}
\catcode`\@=12 % \makeatother

\def\keywords{computers, business, biology, fine art, literature, zoology}

\testkeywordinlist{zoology}{\keywords}{%
  \immediate\write16{* "zoology" found.}%
}{%
  \immediate\write16{* "zoology" not found.}%
}

\end

结果：

• 找到了“动物学”。

Answer 2

你可以使用函数式编程来构建完全可扩展的版本map和字符串比较。但这需要 e-TeX 支持。这里我用来\pdfstrcmp比较字符串，因此此解决方案特定于 pdfTeX。

\def\map#1#2{%
  \domap{#1}#2,\end}

\def\domap#1#2,#3\end{%
  #1{\strip#2\endstrip}%
  \ifx\end#3\end\else\domap{#1}#3\end\fi}

% skips leading spaces
\def\strip#1#2\endstrip{#1#2}

% predicate (pdfTeX specific)
\def\ifstrequal#1#2#3#4{\ifnum\pdfstrcmp{#1}{#4}=0 #2\else #3\fi}

% Check if the list contains something
\def\ifinlist#1#2#3#4{%
  \ifstrequal{found}{#3}{#4}{%
    \map{\ifstrequal{#1}{found}{}}{#2}%
  }%
}

% fully expand \map
\edef\found{%
  \map
    {\ifstrequal{zoology}{``zoology'' found}{}}% predicate with empty false branch
    {computers, business, biology, fine art, literature, zoology}%
}

\tt\meaning\found

% fully expand \ifinlist
\edef\found{%
  \ifinlist
    {zoology}%
    {computers, business, biology, fine art, literature, zoology}%
    {TRUE}%
    {FALSE}%
}

\tt\meaning\found

\bye