The problem is that the \begin{...}
and \end{...}
pair commands automatically create a "group" so that, in effect, the &
and \\
are "out of scope" for the tabular, while inside the "production" environment they just show up at a place where the compiler is not expecting them.
A second problem with your definitions is that, even if they would work, they would be adding an extra \\
at the end of the tabular, adding an unwanted space at the end. Perhaps some more appropriate definitions would be
\documentclass[a4paper,10pt]{article}
\newcommand{\production}[1]{#1 ::= &}
\newenvironment{grammar}{\tabular{p{3cm}l}}{\endtabular}
\begin{document}
\begin{grammar}
\production{XmlStartTag} ... \\
\production{XmlOtherTag} ... \\
\production{XmlEndTag} ...
\end{grammar}
\end{document}
Note no \\
at the end of the last production. Also in the definition of the grammar
you don't need to repeat the work of \begin
/\end
, and you can instead directly use \tabular
and \endtabular
.
The \ifthenelse
condition ends prematurely and leaves an open environment
hanging around in the middle of nowhere.
In conjunction with tcolorbox
environment, the end - delimiter is \endtcolorbox
and I suggest to use two \ifthenelse
statements, one for the start
code of the environment and another one for the end code.
A better approach would use \DeclareTColorbox
, in my opinion or a weird \scantokens
construct.
Also possible: Use \tcolorboxenvironment
to wrap around an existing solution
environment.
\documentclass{article}
\usepackage{ifthen}
\usepackage[most]{tcolorbox}
\newboolean{solution}
\newenvironment{solution}{%
\ifthenelse{\boolean{solution}}{%
\tcolorbox[breakable, width=\textwidth, colframe=red, colback=white]
}{%
}%
}{\ifthenelse{\boolean{solution}}{\endtcolorbox}{}}
\begin{document}
\setboolean{solution}{true}
\begin{solution}
\begin{align*}
x^2 + y^2 &= z^2\\
\Rightarrow x &= \sqrt{z^2 - y^2}\\
&= ...
\end{align*}
\end{solution}
\setboolean{solution}{false}
\begin{solution}
\begin{align*}
x^2 + y^2 &= z^2\\
\Rightarrow x &= \sqrt{z^2 - y^2}\\
&= ...
\end{align*}
\end{solution}
\end{document}
![enter image description here](https://i.stack.imgur.com/4Vdaq.png)
Cleaner solution with two different environments
\documentclass{article}
\usepackage[most]{tcolorbox}
\tcbset{
commonboxes/.style={nobeforeafter},
nobox/.style={commonboxes,blank,breakable},
solutionbox/.style={commonboxes,breakable, colframe=red, colback=white}
}
\newtcolorbox{solutionbox}[1][]{
solutionbox,#1
}
\newtcolorbox{solutionbox*}[1][]{%
nobox,#1
}
\begin{document}
\begin{solutionbox*}
\begin{align*}
x^2 + y^2 &= z^2\\
\Rightarrow x &= \sqrt{z^2 - y^2}\\
&= ...
\end{align*}
\end{solutionbox*}
\begin{solutionbox}
\begin{align*}
x^2 + y^2 &= z^2\\
\Rightarrow x &= \sqrt{z^2 - y^2}\\
&= ...
\end{align*}
\end{solutionbox}
\end{document}
Third installment of a solution with \NewEnviron
and the \BODY
command.
\documentclass{article}
\usepackage{environ}
\usepackage{ifthen}
\usepackage[shortlabels]{enumitem}
\usepackage{amssymb}
\usepackage{mathtools}
\usepackage[most]{tcolorbox}
\newboolean{solution}
\tcbset{
commonboxes/.style={nobeforeafter,breakable},
nobox/.style={commonboxes,blank,breakable},
solutionbox/.style={commonboxes,breakable, colframe=red, colback=white}
}
\NewEnviron{solution}[1][]{%
\ifthenelse{\boolean{solution}}{%
\tcolorbox[solutionbox, width=\textwidth,#1]
\BODY
}{%
}%
}[\ifthenelse{\boolean{solution}}{\endtcolorbox}{}]
\begin{document}
\begin{enumerate}[label={\alph*)}]
\item Compute the Fourier transform of $e^{-|x|}$ for $x\in \mathbb{R}$.
\begin{solution}[colframe=blue]
\begin{align*}
\hat{f}(\xi)&=\frac{1}{\sqrt{2\pi}}\int_{-\infty}^{\infty}e^{-|x|}e^{-ix\xi}dx\\
&=\frac{1}{\sqrt{2\pi}}\int_{0}^{\infty}e^{-x-ix\xi}dx+\int_{-\infty}^0e^{x-ix\xi}dx\\
&=\frac{1}{\sqrt{2\pi}}\int_{0}^{\infty}(e^{-x-ix\xi}-e^{-x+ix\xi})dx\\
&=\frac{1}{\sqrt{2\pi}}[\frac{1}{-(1+i\xi)}(-1)-\frac{1}{-1+i\xi}(-1)]\\
&=\frac{1}{\sqrt{2\pi}}[\frac{1-i\xi}{1+\xi^2}+\frac{-(1+i\xi)}{1+\xi^2}]\\
&=\frac{1}{\sqrt{2\pi}}\frac{-2i\xi}{1+\xi^2}\\
&=-\sqrt{\frac{2}{\pi}}\frac{i\xi}{1+\xi^2}
\end{align*}
\end{solution}
\item Compute the Fourier transform of $e^{-a|x|^2},~a>0$, directly, where $x\in \mathbb{R}$.\\
\begin{solution}
\begin{align*}
\hat{f}(\xi)&=\frac{1}{\sqrt{2\pi}}\int_{-\infty}^{\infty}e^{-a|x|^2}e^{-ix\xi}dx\\
&=\frac{1}{\sqrt{2\pi}}\int_{-\infty}^{\infty}e^{-a(x+\frac{i\xi}{2a})^2+\frac{-\xi^2}{4a}}dx~~~~~~~~x'\doteq x+\frac{i\xi}{2a}\\
&=\frac{1}{\sqrt{2\pi}}e^{-\frac{\xi^2}{4a}}\int_{-\infty}^{\infty}e^{-ax^2}dx\\
&=\frac{e^{-\frac{\xi^2}{4a}}}{2a}
\end{align*}
\end{solution}
\end{enumerate}
\setboolean{solution}{true}
\begin{enumerate}[label={\alph*)}]
\item Compute the Fourier transform of $e^{-|x|}$ for $x\in \mathbb{R}$.
\begin{solution}[colframe=blue]
\begin{align*}
\hat{f}(\xi)&=\frac{1}{\sqrt{2\pi}}\int_{-\infty}^{\infty}e^{-|x|}e^{-ix\xi}dx\\
&=\frac{1}{\sqrt{2\pi}}\int_{0}^{\infty}e^{-x-ix\xi}dx+\int_{-\infty}^0e^{x-ix\xi}dx\\
&=\frac{1}{\sqrt{2\pi}}\int_{0}^{\infty}(e^{-x-ix\xi}-e^{-x+ix\xi})dx\\
&=\frac{1}{\sqrt{2\pi}}[\frac{1}{-(1+i\xi)}(-1)-\frac{1}{-1+i\xi}(-1)]\\
&=\frac{1}{\sqrt{2\pi}}[\frac{1-i\xi}{1+\xi^2}+\frac{-(1+i\xi)}{1+\xi^2}]\\
&=\frac{1}{\sqrt{2\pi}}\frac{-2i\xi}{1+\xi^2}\\
&=-\sqrt{\frac{2}{\pi}}\frac{i\xi}{1+\xi^2}
\end{align*}
\end{solution}
\item Compute the Fourier transform of $e^{-a|x|^2},~a>0$, directly, where $x\in \mathbb{R}$.\\
\begin{solution}
\begin{align*}
\hat{f}(\xi)&=\frac{1}{\sqrt{2\pi}}\int_{-\infty}^{\infty}e^{-a|x|^2}e^{-ix\xi}dx\\
&=\frac{1}{\sqrt{2\pi}}\int_{-\infty}^{\infty}e^{-a(x+\frac{i\xi}{2a})^2+\frac{-\xi^2}{4a}}dx~~~~~~~~x'\doteq x+\frac{i\xi}{2a}\\
&=\frac{1}{\sqrt{2\pi}}e^{-\frac{\xi^2}{4a}}\int_{-\infty}^{\infty}e^{-ax^2}dx\\
&=\frac{e^{-\frac{\xi^2}{4a}}}{2a}
\end{align*}
\end{solution}
\end{enumerate}
\end{document}
The \BODY
command contains the environment 'text' and is printed only in the case solution
is true.
Best Answer
I'm not sure why but you can't use
\begin{align}
and\end{align}
in the definition of a new environment; you have to use the "lower-level" macros\align
and\endalign
instead. Edit: as pointed by alexwlchan in his comment, you can find more details about that in section 6 of Technical notes on theamsmath
package.Here I've used the equivalent of an
align*
environment (see Herbert's answer to Define a custom align, and align* environment).Note that you will get an error if you try to reset your
grammarcounter
at each chapter in thearticle
class, because the latter doesn't have chapters;\section
is the most high-level sectioning command in thearticle
class. Did you meaninstead?