Shifting nested tikz scopes with a command

Question

I try to automate some things with tikz, and I am running into a problem that I do not understand. Nesting scopes with shifts defined as commands does not work as I was expecting.

For example, this works perfectly :

\begin{tikzpicture}
\def\coord{(1,0)}
\begin{scope}[shift={\coord}]
\end{scope}
\begin{scope}[shift={\coord}]
\end{scope}
\end{tikzpicture}

and it works correctly, as one can see by adding some \node[fill,circle] at (0,0) {}; inside and outside the scopes

but the following fails :

\begin{tikzpicture}
\def\coord{(1,0)}
\begin{scope}[shift={\coord}]
  \begin{scope}[shift={\coord}]
  \end{scope}
\end{scope}
\end{tikzpicture}

However, this

\begin{tikzpicture}
\def\coord{(1,0)}
\begin{scope}[shift={(1,0)}]
  \begin{scope}[shift={(1,0)}]
  \end{scope}
\end{scope}
\end{tikzpicture}

indeed works. I do not understand what is happening. pdflatex returns

Package tikz Error: Cannot parse this coordinate.
See the tikz package documentation for explanation. ...

in the problematic case. The question is why does this happen ? I probably did something wrong, but I really do not see what.

Notice that adding length units does not fix the problem. However, a similar problem with xshift and yshift does not seem to happen. Also notice that I tried to simplify the code as much as possible ; that's why it draws nothing.

Thanks,

Answer 1

As qrrbrbirlbel noted TikZ works with parsing letter-by-letter the command stream. It is a blessing and sometimes a curse depending on the context and when key value system is mixed with macros and literal text. So you can give a hand to TikZ to understand what it should read. So changing your definition without the parentheses is enough for it to go, oh, that must be a coordinate then

Also notice that braces are needed to hide the commas and brackets in the options and you can remove them here, so this doesn't cost you extra typing.

\begin{tikzpicture}
\draw[style=help lines] (0,-1) grid[step=1cm] (4,1);
\def\coord{1,0}
\begin{scope}[shift=(\coord)]
  \begin{scope}[shift=(\coord)]
      \begin{scope}[shift=(\coord)]
        \begin{scope}[shift=(\coord)]
        \node (a) at (0,0) {a};
        \end{scope}
      \end{scope}
  \end{scope}
\end{scope}
\end{tikzpicture}