在lua中构建Latex/Tex参数（2）

与 Building Lates/Tex arguments in lua 相同的问题，但是更加复杂：

第二部分 更合适的模型： 我试图将绘图参数替换为 Lua 生成： 原始的：

\begin{tikzpicture}[line cap=round,line join=round,>=triangle 45,x=1.0cm,y=1.0cm]
\draw[smooth,samples=100,domain=-3.0:2.0] plot(\x,{(\x-1.0)^2.0*(\x+3.0)});
\end{tikzpicture}%

手工宏的替换：工作正常

\def\tempD{(\x-1)*(\x-1)*(\x+3)}
\begin{tikzpicture}[line cap=round,line join=round,>=triangle 45,x=1.0cm,y=1.0cm]
\draw[smooth,samples=100,domain=-3.0:2.0] plot(\x,{\tempD}); % works fine
\end{tikzpicture}%

使用 Lua 生成的字符串替换手工宏的尝试：仍在寻找正确的解决方法

\begin{tikzpicture}[line cap=round,line join=round,>=triangle 45,x=1.0cm,y=1.0cm]
%\draw[smooth,samples=100,domain=-3.0:2.0] plot(\x,{\strfunc??????}); % the correct \strfuncXX is still to be found !
\end{tikzpicture}%

尝试找到正确的 \strfuncXX，参考 egreg 的信息：

\def\strfuncA{\luaexec{tex.write("(\\x-1)*(\\x-1)*(\\x+3)")}} % fails in draw, probably because it is not expanded enough as an argument of draw
%\edef\strfuncAA{\luaexec{tex.write("(\\x-1)*(\\x-1)*(\\x+3)")}} % fails because \luaexec non expandable
\def\strfuncB{\directlua{tex.write("(\\x-1)*(\\x-1)*(\\x+3)")}} % fails because \directlua has a problem managing the "\\"
\def\strfuncC{\directlua{tex.write("(x-1)*(x-1)*(x+3)")}}
\edef\strfuncCC{\directlua{tex.write("(x-1)*(x-1)*(x+3)")}} % works fine ... except that we get an expression with xs instead of \xs
\def\strfuncD{\directlua{tex.write("(\string\ x-1)*(\string\ x-1)*(\string\ x+3)")}} % \strfuncD fails (why ?)
%\edef\strfuncDD{\directlua{tex.write("(\string\ x-1)*(\string\ x-1)*(\string\ x+3)")}} % \strfuncD fails so \edef will fail

从 \luaexec 移动到 \luadirect（或 \directlua）会产生一个问题，即我必须生成我无法解决的强制性 \x。