Loop Through Array of Strings (Actually an Array of Array of Strings, e.g. `{{black, ab}, {white, cd}}`)

Question

I'm drawing stones on a Go (game) board with SGF coordinates (which I only managed to do from the the help people gave me on this question) like this \drawStoneFromSgfCoords{ab}.

However, there might be many stones per diagram, so it would be practical to also have another macro like this: \drawStonesFromSgfCoords{{black, ab}, {white, cd}} (the colors typically alternate, but sometimes it's more practical to have a list of black coordinates and then white's).

Here's what I'm trying right now, though it doesn't work (I mean, it does work, just not with the new macro):

\documentclass{article}
\usepackage{tikz}
% From this answer by @DavidCarlisle.
\newcommand\notwhite{black}
\newcommand\notblack{white}
% From this answer by @DavidCarlisle.
\ExplSyntaxOn
  \cs_generate_variant:Nn \int_from_alph:n {e}
\newcommand\stringToCoordX[1]{
    \int_from_alph:e{\use_i:nn#1}
  }
  \newcommand\stringToCoordY[1]{
    ~\int_from_alph:e{\use_ii:nn#1}
  }
\ExplSyntaxOff
\newcommand{\drawStoneFromSgfCoords}[2]{
  \pgfmathsetmacro{\x}{\stringToCoordX{#2} - 1}
  \pgfmathsetmacro{\y}{\stringToCoordY{#2} - 1}
\draw[draw = \UseName{not#1}, fill = #1, line width = 0.1mm]
    (\x * 10cm / 18, \y * 10cm / 18)
    circle [radius = 0.2575cm];
    node[color = white] {1};
}
% Example usage: drawStonesFromSgfCoords{{black, ab}, {white, cd}}
\newcommand{\drawStonesFromSgfCoords}[1]{
  \foreach \coords in {#1}{
    \drawStoneFromSgfCoords{{\coords}[0]}{{\coords}[1]}
  }
}
\begin{document}
  \begin{tikzpicture}
    \pgfmathsetmacro{\step}{10 / 18}
\draw[step=\step] (0, 0) grid (10, 10);

\drawStoneFromSgfCoords{black}{ab}
\drawStoneFromSgfCoords{white}{cd}

% \drawStonesFromSgfCoords{{black, ab}, {white, cd}}

\end{tikzpicture}
\end{document}

What's the proper way of accessing or passing arrays (within a loop)?

(I'm using PGF's \foreach because that's what I know.)

Answer 1

I think, it is a better idea to process the nested clist (a comma-separated list) via expl tools here since tools already exist there to handle such lists:

\documentclass{article}
\usepackage{tikz}
% From this answer by @DavidCarlisle.
\newcommand\notwhite{black}
\newcommand\notblack{white}
% From this answer by @DavidCarlisle.
\ExplSyntaxOn
  \cs_generate_variant:Nn \int_from_alph:n {e}
\NewExpandableDocumentCommand{\stringToCoordX}{ m }{
    \int_from_alph:e { \use_i:nn #1 }
  }
  \NewExpandableDocumentCommand{\stringToCoordY}{ m }{
    \int_from_alph:e { \use_ii:nn #1 }
  }
\ExplSyntaxOff
\newcommand{\drawStoneFromSgfCoords}[2]{
  \pgfmathsetmacro{\x}{\stringToCoordX{#2} - 1}
  \pgfmathsetmacro{\y}{\stringToCoordY{#2} - 1}
\draw[draw = \UseName{not#1}, fill = #1, line width = 0.1mm]
    (\x * 10cm / 18, \y * 10cm / 18)
    circle [radius = 0.2575cm];
}
\ExplSyntaxOn
  % Example usage: drawStonesFromSgfCoords{{black, ab}, {white, cd}}
  \NewExpandableDocumentCommand{\drawStonesFromSgfCoords}{ m }{
    \clist_set:Nn \l_tmpa_clist { #1 }
    \clist_map_inline:Nn \l_tmpa_clist {
      \clist_set:Nn \l_tmpb_clist { ##1 }
      \clist_pop:NN \l_tmpb_clist \l_tmpa_tl 
      \clist_pop:NN \l_tmpb_clist \l_tmpb_tl 
      \exp_args:Noo \drawStoneFromSgfCoords { \l_tmpa_tl } { \l_tmpb_tl }
}

}
\ExplSyntaxOff
\begin{document}
  \begin{tikzpicture}
    \pgfmathsetmacro{\step}{10 / 18}
\draw[step=\step] (0, 0) grid (10, 10);

%\drawStoneFromSgfCoords{black}{ab}
%\drawStoneFromSgfCoords{white}{cd}
\drawStonesFromSgfCoords{{black, ab}, {white, cd}}


\end{tikzpicture}
\end{document}

---

Some notes on the used commands (a nice overview and an exhaustive documentation can be found in the L3 Interfaces PDF):

• \clist_set:Nn \l_tmpa_clist { #1 } stores a clist (a comma-separated list) in a token variable to make it accessible. In the example case, {{black, ab}, {white, cd}} is stored as clist in the token variable \l_tmpa_clist.
• \clist_map_inline:Nn \l_tmpa_clist { ... } loops over every item in the clist (stored in the token variable) and executes the code between the curly braces. The current item is accessed via #1 (##1 in the code example, because it is nested one level deeper).
• \clist_pop:NN \l_tmpb_clist \l_tmpa_tl grabs the first item of the clist and stores it in a token variable (l_tmpa_tl). It then removes this item from the clist.
• \exp_args:Noo \drawStoneFromSgfCoords { \l_tmpa_tl } { \l_tmpb_tl } first expands the two token variables and inserts the result as arguments to \drawStoneFromSgfCoords.

So, lets look what happens step by step if we say \drawStonesFromSgfCoords{{black, ab}, {white, cd}}:

\NewExpandableDocumentCommand{\drawStonesFromSgfCoords}{ m }{
% store {{black, ab}, {white, cd}} in \l_tmpa_clist 
\clist_set:Nn \l_tmpa_clist { #1 }

% loop over items in \l_tmpa_clist 
\clist_map_inline:Nn \l_tmpa_clist {

  % store {black, ab} in \l_tmpb_clist
  \clist_set:Nn \l_tmpb_clist { ##1 }

  % store black in \l_tmpa_tl and remove item from clist
  \clist_pop:NN \l_tmpb_clist \l_tmpa_tl 

  % store ab in \l_tmpb_tl and remove item from clist
  \clist_pop:NN \l_tmpb_clist \l_tmpb_tl 

  % expand \l_tmpa_tl and \l_tmpb_tl so that we get
  % \drawStoneFromSgfCoords{black}{ab}
  \exp_args:Noo \drawStoneFromSgfCoords { \l_tmpa_tl } { \l_tmpb_tl }

  % repeat this loop for the next item in the clist in \l_tmpa_clist

}

}