Problems expanding a variable inside a `\foreachitem` using the package `listofitems` and a macro

Question

Following this answer by @StevenB.Segletes, who's also one of the creators of the package listofitems, I'm now trying to use what that package was able to parse from a single-branch SGF string inside a macro.

This is what I would like to be able to achieve, but I think I'm having expansion problems, because I'm getting a Missing \endcsname inserted error:

\long\def\Firstof#1#2\endFirstof{#1}
\ignoreemptyitems
\newcommand{\parseSgf}[1]{
  \setsepchar{;/[||]}
  \readlist*\Z{#1}
% This loop basically splits on ;, which is a node/move delimiter in SGF
  \foreachitem \i \in \Z[]{
    \itemtomacro\Z[\icnt, 1]\stoneColor
    \itemtomacro\Z[\icnt, 2]\sgfCoords
% These if's test the `key[value]` SGF format for the keys `B` and `W`, which denote Black and White moves, respecitvely
% Other keys typically refer to metadata, or other secondary info.
\if\stoneColor B
  \drawStoneFromSgfCoords{black}{\sgfCoords} % if I hardcode the arguments, it works.
  % \drawStoneFromSgfCoords{black}{Z[\icnt, 2]} % I've also tried stuff like this directly...
\fi
\if\stoneColor AB
  \drawStoneFromSgfCoords{black}{\sgfCoords}
\fi
\if\stoneColor W
  \drawStoneFromSgfCoords{white}{\sgfCoords}
\fi
\if\stoneColor AW
  \drawStoneFromSgfCoords{white}{\sgfCoords}
\fi

}
}

Ideally, if anyone is able to find a solution to this, I would like it to find both Black or White moves (B and W) and edited (added) stones (AB and AW), so the if's would look like this:

\if\stoneColor { B \OR AB }
...
\if\stoneColor { W \OR AW }

But, of course, I can save this for another question, if it gets to be too much.

---

Here's a complete example:

\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];
}
\usepackage{listofitems}
% From this answer by @StevenB.Segletes.
\long\def\Firstof#1#2\endFirstof{#1}
\ignoreemptyitems
\newcommand{\parseSgf}[1]{
  \setsepchar{;/[||]}
  \readlist*\Z{#1}
\foreachitem \i \in \Z[]{
    \itemtomacro\Z[\icnt, 1]\color
    \itemtomacro\Z[\icnt, 2]\sgfCoords
\expandafter\if\expandafter\Firstof\stoneColor\endFirstof B
  \drawStoneFromSgfCoords{black}{ab}
\else\expandafter\if\expandafter\Firstof\stoneColor\endFirstof W
  \drawStoneFromSgfCoords{white}{cd}
\fi\fi

}
}
\def\sgfA{;B[ab];W[cd]} % not truly valid SGF, just one simple example
\def\sgfB{(;GM[1]FF[4]CA[UTF-8]AP[Sabaki:0.52.2]KM[6.5]SZ[19]DT[2024-02-05];B[as];W[bs];B[cs])}
\def\sgfC{(;GM[1]FF[4]CA[UTF-8]AP[Sabaki:0.52.2]KM[6.5]SZ[19]DT[2024-02-05];B[as];W[bs];B[cs];PL[W]AB[dq]AW[eq])}
\begin{document}
  \begin{tikzpicture}
    \pgfmathsetmacro{\step}{10 / 18}
\draw[step=\step] (0, 0) grid (10, 10);

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

\parseSgf{\sgfA}

\end{tikzpicture}
\end{document}

Answer 1

Several issues:

1. Don't use \color, since it overwrites an existing macro...I changed it to \Color.

2. The value of \Color will be B or W, which is not an actual color. Therefore, I introduce \newcommand\thecolorofB{black} and \newcommand\thecolorofW{white} to convert \Color into an actual color.

3. The parentheses in the SGF definitions are also causing a problem. They were not being parsed, but instead interpreted as SGF commands (but missing the associated [] datum). Therefore, I hardwired the parsing to digest them away. This approach solves the immediate issue, but may not be suitable depending on where you want to take this problem in the future.

4. The values of \Color and \sgfCoords needed to be expanded, prior to feeding them to your macro \drawStoneFromSgfCoords. I accomplished this by expanding them into \tmp and then expanding \tmp into the macro invocation.

The MWE:

\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];
}
\usepackage{listofitems}
% From this answer by @StevenB.Segletes.
\long\def\Firstof#1#2\endFirstof{#1}
\newcommand\thecolorofB{black}
\newcommand\thecolorofW{white}
\ignoreemptyitems
\newcommand{\parseSgf}[1]{%
  \setsepchar{;||(||)/[||]}%
  \readlist*\Z{#1}%
%
  \foreachitem \i \in \Z[]{%
    \itemtomacro\Z[\icnt, 1]\Color
    \itemtomacro\Z[\icnt, 2]\sgfCoords
    \edef\tmp{{\csname thecolorof\Color\endcsname}{\sgfCoords}}%
%
    \expandafter\if\expandafter\Firstof\Color\endFirstof B
      \expandafter\drawStoneFromSgfCoords\tmp
    \else\expandafter\if\expandafter\Firstof\Color\endFirstof W
      \expandafter\drawStoneFromSgfCoords\tmp
    \fi\fi
  }%
}
\def\sgfA{;B[ab];W[cd]}
\def\sgfB{(;GM[1]FF[4]CA[UTF-8]AP[Sabaki:0.52.2]KM[6.5]SZ[19]DT[2024-02-05];B[as];W[bs];B[cs])}
\def\sgfC{(;GM[1]FF[4]CA[UTF-8]AP[Sabaki:0.52.2]KM[6.5]SZ[19]DT[2024-02-05];B[as];W[bs];B[cs];PL[W]AB[dq]AW[eq])}
\begin{document}
  \begin{tikzpicture}
    \pgfmathsetmacro{\step}{10 / 18}
    \draw[step=\step] (0, 0) grid (10, 10);
    \parseSgf{\sgfC}
  \end{tikzpicture}
\end{document}