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My question is about declaring a "newcommand" with an option.

I have defined

\newcommand{\bforall}[2]{\forall #1\, (#2)}

so that $\bforall{x}{x \in A}$ writes $\forall x (x \in A)$.

I would like some control over the brackets. Namely, I would like 

\bforall[s]{x}{x \in A}

to use square braces, and

\bforall[c]{x}{x \in A}

to use curly braces.

How can this be accomplished?

I've search the forum and found 1/ Different command definitions with and without optional argument and 2/ Optional argument for newcommand? and neither helped me.

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4 Answers 4

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Here is a way, without packages.

\documentclass{article} \newcommand\bforall[3][r]{% \ifx r#1\forall #2\, (#3)\else \ifx s#1\forall #2\, [#3]\else \ifx c#1\forall #2\, \{#3\}\else \mathrm{Illegal~option}% \fi\fi\fi } \begin{document} $\bforall{x}{x \in A}$ $\bforall[r]{x}{x \in A}$ $\bforall[s]{x}{x \in A}$ $\bforall[c]{x}{x \in A}$ \end{document}

enter image description here

As touhami rightly points out, the penalty for using the simplicity of the \ifx construct is that an accidental syntax error such as using a two character optional argument like [rs] will not produce an error message, but rather just wrongly set the term.

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  • see @egreg comment to my answer tex.stackexchange.com/questions/254158/… Commented Aug 4, 2015 at 3:12
  • @touhami I see the point, but I'm not sure if it applies, since my optional argument has a default non-empty value. To run into the problem, one would have to pass a blank optional argument, I think. But it certainly doesn't hurt to add a \relax after #1 to address that case. In fact, I just tried the case, and it throws the expected error already. Commented Aug 4, 2015 at 9:50
  • Sorry, i mean @egreg's last comment, in this case $\bforall[rs]{x}{x \in A}$ Commented Aug 4, 2015 at 10:04
  • @touhami In your case, the optional argument was a mathematical term that could be one or more characters. In my case, the optional argument is a single letter indicating round, square, or curly braces. A 2-character optional argument in my case is indicative of a syntax error. Commented Aug 4, 2015 at 10:12
  • here is the prolem $\bforall[rs]{x}{x \in A}$ will not idicate error. Commented Aug 4, 2015 at 10:46
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Here is one way to do that using the xstring package's \IfStrEqCase:

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The default option is round braces, curly braces and square braces. You can also add an optional second parameter to control the brace size:

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Code:

\documentclass{article} \usepackage{xstring} \newcommand{\bforall}[3][r]{% \forall #2\, \IfStrEqCase{#1}{% {r}{(#3)}% {c}{\{#3\}}% {s}{{[#3]}}% }[% %% Issue error message here about unsuported bracket type ]% } \begin{document} $\bforall{x}{x \in A}$ $\bforall[r]{x}{x \in A}$ $\bforall[c]{x}{x \in A}$ $\bforall[s]{x}{x \in A}$ \end{document}

Code Resizing Brackets:

\documentclass{article} \usepackage{xstring} \usepackage{xparse} \usepackage{amsmath} \NewDocumentCommand{\bforall}{% O{r}% #1 = r, c or s (bracket shape) O{}% #2 = optional size specifier m% #3 m% #4 }{% \forall #3\, \IfStrEqCase{#1}{% {r}{#2(#4#2)}% {c}{#2\{#4#2\}}% {s}{{#2[#4#2]}}% }[% %% Issue error message here about unsupported bracket type \PackageError{tree}{Undefined option to tree: #1}{} ]% } \begin{document} \begin{minipage}{0.25\linewidth} $\bforall{x}{x \in A}$ $\bforall[r]{x}{x \in A}$ $\bforall[c]{x}{x \in A}$ $\bforall[s]{x}{x \in A}$ \end{minipage} \hspace*{0.5cm} \begin{minipage}{0.25\linewidth} $\bforall[r][\Big]{x}{x \in A, x > \dfrac{1}{2}}$ $\bforall[c][\Big]{x}{x \in A, x > \dfrac{1}{2}}$ $\bforall[s][\bigg]{x}{x \in A, x > \dfrac{1}{2}}$ \end{minipage} \end{document}
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For a case switch macro the best is expl3; I used the letters already common with amsmath, p for parentheses, b for brackets, B for braces.

\documentclass{article} \usepackage{amsmath} \usepackage{xparse} \ExplSyntaxOn \NewDocumentCommand{\bforall}{O{p}mm} { \forall #2\, \str_case:nnF { #1 } { {p}{(#3)} {b}{[#3]} {B}{\{#3\}} } {\@latex@error{Illegal~option~#1}{I~used~p}} } \ExplSyntaxOff \begin{document} $\bforall{x}{x \in A}$ $\bforall[p]{x}{x \in A}$ $\bforall[b]{x}{x \in A}$ $\bforall[B]{x}{x \in A}$ \end{document}

enter image description here

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A plain TeX one with a different syntax

\def\bforall#1{\forall#1\,\futurelet\tmptoken\dobforall} \def\dobforall{\ifx\tmptoken\bgroup\expandafter\bforallbraces\fi \ifx\tmptoken[\expandafter\bforallbrackets\fi \ifx\tmptoken(\expandafter\bforallparenthesis\fi \relax} \def\bforallbraces#1\relax#2{\{#2\}} \def\bforallbrackets#1\relax[#2]{[#2]} \def\bforallparenthesis#1\relax(#2){(#2)} $\bforall{x}(x \in A)$\par $\bforall{x}{x \in A}$\par $\bforall{x}[x \in A]$\par \bye

enter image description here

You can use those definitions also in LaTeX without the need of any package. The syntax seems easier for me \bforall{x}(x\in A), \bforall{x}{x\in A} and \bforall{x}[x\in A]. In any case, for your needs, may be you don't need that macro at all, just \def\bforall#1{\forall#1\,} and then it's followed by whatever you input?

With a little bit of refinement to let you use \bforall x {x \in A} syntax. (In LaTeX it would be easier because of \@ifnextchar.)

\def\bforall#1{\forall#1\,\futurelet\tmptoken\dobforall} \def\dobforall{\ifx\tmptoken\spacetoken\expandafter\bforallspace\fi \ifx\tmptoken\bgroup\expandafter\bforallbraces\fi \ifx\tmptoken[\expandafter\bforallbrackets\fi \ifx\tmptoken(\expandafter\bforallparenthesis\fi \relax} \def\bforallbraces#1\relax#2{\{#2\}} \def\bforallbrackets#1\relax[#2]{[#2]} \def\bforallparenthesis#1\relax(#2){(#2)} \def\bforallspace#1\relax{\dobforallspace} \expandafter\def\expandafter\dobforallspace\space{\futurelet\tmptoken\dobforall} \lowercase{\let\spacetoken= } % $\bforall x (x \in A)$\par $\bforall x {x \in A}$\par $\bforall x [x \in A]$\par \bye
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