Macro expansion in TikZ node

Question

I am having some problems with macro expansion in TikZ nodes. The MWE below is supposed to draw nodes at specified coordinates and display their coordinate rounded to the nearest number, but it shows the coordinates of the last node for both of them.

\documentclass[]{article}

\usepackage{pgfplots}
\usepackage{xparse}

\ExplSyntaxOn

\tl_new:N \x
\tl_new:N \x_round

\NewDocumentCommand \mynode { m } {
    \tl_set:Nn \x { 
        \fp_eval:n { #1 } 
    }

    \tl_set:Nn \x_round { 
       \fp_eval:n { round ( \x ) } 
    }

    \addplot [style={mark=none}] coordinates { ( \x , \x ) } node { \x_round } ;
}

\ExplSyntaxOff

\begin{document}
    \begin{tikzpicture}
        \begin{axis}            
            \mynode{1.1}
            \mynode{2.2}
        \end{axis}
    \end{tikzpicture}
\end{document}

I assume the problem is that the \x_round is not expanded in the node until the end of the environments. How can I ensure \x_round is expanded immediately?

I have noticed that replacing the command with

\NewDocumentCommand \mynode { m } {
    \addplot [style={mark=none}] coordinates { ( #1 , #1 ) } node { \fp_eval:n { round ( #1 ) }  } ;
}

does fix the problem, but for my real code, it is inadequate as the code is more complex.

Answer 1

You should use \tl_set:Nx, but it's quite pointless anyway:

\documentclass{article}

\usepackage{pgfplots}
\usepackage{xparse}

\ExplSyntaxOn

\NewDocumentCommand \mynode { m }
 {
  \addplot [style={mark=none}]
    coordinates { ( \fp_eval:n { #1 } , \fp_eval:n { #1 } ) }
    node { \fp_eval:n { round(#1) } } ;
 }

\ExplSyntaxOff

\begin{document}

\begin{tikzpicture}
  \begin{axis}
    \mynode{1.1}
    \mynode{2.2}
  \end{axis}
\end{tikzpicture}

\end{document}

Avoid names such as \x and \x_round, use the proper naming conventions.

You can use variables (here I use fp ones, but tl can be good as well, provided you set them with \tl_set:Nx). However, text in the node has to be expanded before passing it to PGF:

\documentclass{article}

\usepackage{pgfplots}
\usepackage{xparse}

\ExplSyntaxOn

\fp_new:N \l_slo_coord_x_fp
\fp_new:N \l_slo_coord_x_round_fp

\NewDocumentCommand \mynode { m }
 {
  \fp_set:Nn \l_slo_coord_x_fp { #1 }
  \fp_set:Nn \l_slo_coord_x_round_fp { round ( \l_slo_coord_x_fp ) }
  \use:x
   {
    \exp_not:N \addplot [style={mark=none}]
      coordinates { ( \fp_use:N \l_slo_coord_x_fp , \fp_use:N \l_slo_coord_x_fp ) }
      node { \fp_use:N \l_slo_coord_x_round_fp } ;
   }
 }

\ExplSyntaxOff

\begin{document}

\begin{tikzpicture}
  \begin{axis}
    \mynode{1.1}
    \mynode{2.2}
  \end{axis}
\end{tikzpicture}

\end{document}