How do I process a command parameter into a certain number of characters?

Question

Currently, I’m in the process of writing a travel guide and I’d like to include general price information next to the locations and events, e.g.

$$$$ - Fancy Expensive Steakhouse

I figured that since I’d be doing this a lot it’d be a good idea to make a little command to insert an arbitrary number of dollar signs instead of individually escaping each dollar sign, but for the life of me I couldn’t figure it out.

Ideally, I’d want the command to go something like

\price{4}

To insert 4 dollar signs like in the above. I feel like I’m missing something simple, but after googling various variations of my question and looking into tex macros (unfortunately unfruitfully) I’m still at a loss. I’d also like to be able to format the dollar symbols (in gray for instance), but I feel like I can do that by defining an environment around the \price command once I get it working.

Any help or pointers to relative documentation would be greatly appreciated. Thanks!

Answer 1

One way is to have a simple recursion on the number

\documentclass{article}
\begin{document}
\newcommand\price[1]{\ifnum#1>0\$\price{\numexpr#1-1\relax}\fi}
\price{1}  zzz
\price{20} ZZZ
\end{document}

Answer 2

It's better to separate \price and \pricesymbol.

\documentclass{article}
\usepackage{xcolor}
\NewDocumentCommand{\pricesymbol}{}{\textcolor{black!60}{$}}
\ExplSyntaxOn
\NewDocumentCommand{\price}{m}
 {
  \prg_replicate:nn { #1 } { \pricesymbol }
 }
\ExplSyntaxOff
\begin{document}
\price{4} -- Fancy Expensive Steakhouse
\price{2} -- Pizza House (no pineapple)
\end{document}

You can even have fractional price symbols.

\documentclass{article}
\usepackage{xcolor}
\usepackage{trimclip}
\NewDocumentCommand{\pricesymbol}{}{\textcolor{black!60}{$}}
\ExplSyntaxOn
\NewDocumentCommand{\price}{m}
 {
  \prg_replicate:nn { \fp_eval:n { trunc(#1,0) } } { \pricesymbol }
  \fp_compare:nT { #1 - trunc(#1,0) > 0 }
   {
    \clipbox{0~0~{\fp_eval:n { 1 - #1 + trunc(#1,0) }\width}~0} { \pricesymbol } ,
   }
 }
\ExplSyntaxOff
\begin{document}
\price{4} -- Fancy Expensive Steakhouse
\price{2} -- Pizza House (no pineapple)
\price{2.3} -- Pizza House (no pineapple)
\price{2.5} -- Pizza House (no pineapple)
\price{2.7} -- Pizza House (no pineapple)
\end{document}

Answer 3

Tail-recursive, only traditional TeX:

\documentclass{article}
\newcommand\priceloop[1]{\if#1m$\expandafter\priceloop\fi}
\newcommand\price[1]{\expandafter\priceloop\romannumeral\number\number#1 000\relax}
\begin{document}
\price{12}
\end{document}

Tail-recursive, eTeX-extensions:

\documentclass{article}
\newcommand\exchange[2]{#2#1}%
\newcommand\price[1]{\ifnum#1>0 \exchange{$\expandafter\price\expandafter{\the\numexpr#1-1\relax}}\fi}
\begin{document}
\price{12}
\end{document}

Or use one of David Kastrup's \replicate-variants:

\documentclass{article}
\newcommand\gobble[1]{}
\newcommand\xii[2]{\if#2m#1\expandafter\xii\else\expandafter\gobble\fi{#1}}
\newcommand\xiii[2]{\xii{#2}#1\relax}
\newcommand\replicate[1]{\expandafter\xiii\expandafter{\romannumeral\number\number#1 000}}%
\newcommand\price[1]{\replicate{#1}{$}}
\begin{document}
\price{12}
\end{document}

\documentclass{article}

\newcommand\recur[1]{\csname rn#1\recur}
\newcommand\rnm[1]{\endcsname{#1}#1}
\newcommand\rn[1]{}
\newcommand\replicate[1]{\csname rn\expandafter\recur\romannumeral\number\number#1 000\endcsname\endcsname}

\newcommand\price[1]{\replicate{#1}{\$}}

\begin{document}

\price{12}

\end{document}

The sequence \romannumeral\number\number#1 000 instead of just \romannumeral#1000 is for the following reason:

#1 is to be some TeX-⟨number⟩-quantity that is to be multiplied by 1000 by attaching digits 000 so that \romannumeral delivers the corresponding amount of character-tokens m.

#1 is not necessarily a sequence of digits.

It could be a \count-register as well where you need a space-token for separating the number denoting the \count-register from the three zeros to attach to the tokens forming the value held in that \count-register:

Assume you wish to denote the value held in \count-register 17:

\romannumeral\count17000 will not work out because TeX assumes an attempt of denoting the value held in \count-register 17000 and raises an error as there is no \count-register 17000.

\romannumeral\number\number\count17 000 does work out:

The second \number delivers the value that is held in \count-register 17 as digit-sequence. The space behind 17/before 000 is consumed as end-marker of the digit-sequence 17 denoting the \count-register.

The first \number is not needed here/does not change the fact that when the second \number is finished you already have a digit-sequence with three zeros appended which can be processed by \romannumeral.

But the TeX-⟨number⟩-quantity could be a \countdef-token or a \chardef-token or the like as well whereafter a space-token will not be removed by TeX.

Assume someone doing \chardef\sixtyfive=`\A.
\romannumeral\sixtyfive000 will not work out because due to TeX's rules for gathering TeX-⟨number⟩-quantities with \chardef-tokens 000 will not be considered part of the number to be processed by \romannumeral.

But \romannumeral\number\number\sixtyfive⟨space-token⟩000 will work out:

The second \number delivers 65 from the chardef-token \sixtyfive. This 65 is trailed by the ⟨space-token⟩ and the three zeros. The first \number finds the digit-sequence 65 trailed by a ⟨space-token⟩ and eliminates that ⟨space-token⟩. Now \romannumeral as number to convert can gather 65000 and deliver 65 characters m.