Unwanted space around def-generated tabular

Question

I'm using some code I found to generate, from simple input, a nicely formatted list of steps in solving an equation. However, my method is adding unwanted space to the left and at the bottom of the result. Please have a look:

\documentclass{article}

\usepackage{xstring} % using: StrSubstitute

% equation solving list
\renewcommand\equation[1]{
\everymath{\displaystyle}
\renewcommand{\arraystretch}{2.5}
\begin{tabular}{@{}r@{}c@{}l@{}}
\foreach{\makeeq}{}{#1}
\end{tabular}\\
}

% equation helper function (first parameter is unused)
\def\makeeq#1#2{
\saveexpandmode\expandarg
\StrSubstitute[1]{#2}{=}{$&$\ =\ $&$}[\subbed]
\restoreexpandmode
\subbed\\
}

% % % FOREACH % % %

\makeatletter

% Functional foreach construct 
% #1 - Function to call on each comma-separated item in #3
% #2 - Parameter to pass to function in #1 as first parameter
% #3 - Comma-separated list of items to pass as second parameter to function #1
\def\foreach#1#2#3{%
\@test@foreach{#1}{#2}#3,\@end@token%
}

% Internal helper function - Eats one input
\def\@swallow#1{}

% Internal helper function - Checks the next character after #1 and #2 and 
% continues loop iteration if \@end@token is not found 
\def\@test@foreach#1#2{%
\@ifnextchar\@end@token%
 {\@swallow}%
 {\@foreach{#1}{#2}}%
}

% Internal helper function - Calls #1{#2}{#3} and recurses
% The magic of splitting the third parameter occurs in the pattern matching of the \def
\def\@foreach#1#2#3,#4\@end@token{%
#1{#2}{#3}%
\@test@foreach{#1}{#2}#4\@end@token%
}

\makeatother

% % % % % %

\begin{document}

desired result: \
start

\everymath{\displaystyle}
\renewcommand{\arraystretch}{2.5}
\begin{tabular}{@{}r@{}c@{}l@{}}
$ X $&$\ =\ $&$ 1 + 1 $ \\
$ $&$\ =\ $&$ 2 $ \\
\end{tabular}\
end

\bigskip
actual result: \
start

\equation{
$ X = 1 + 1 $,
$ = 2 $
}

end

\end{document}

The output:

I can't figure out what's adding the whitespace. Any help would be appreciated. Thanks!

Answer 1

The particular problem here is that your macros are introducing some extra spaces. LaTeX sometimes interprets newlines as spaces, and so by ending lines with the % character, you can stop these being introduced. In your case, fix your \makeeq macro like so to get your desired output:

% equation helper function (first parameter is unused)
\def\makeeq#1#2{%  <--- added
\saveexpandmode\expandarg
\StrSubstitute[1]{#2}{=}{$&$\ =\ $&$}[\subbed]%    <--- added
\restoreexpandmode
\subbed\\
}

Answer 2

The unwanted vertical space comes from the \\ in the definition of \makeeq, that when the for-each loop is ended, \@swallow will insert a "nothing" as the third row of your table. You should consider taking out the \\ from the definition and write \equation{$ X = 1 + 1 $\\,$ = 2 $} instead.