Macro shortcut for \mathrm command

Question

I am attempting to make a macro shortcut for the \mathrm command from amsmath.

My idea is that in lieu of writing, for example, \mathrm{R} to get the Roman R in math mode, I'd like to enter \RR instead. Likewise, suppose I wanted Roman P, I'd like instead to enter \PP.

The following MWE gets me the Roman R symbol, but I'd like this to be maximally flexible for any letter without having to define 52 separate \aa, \bb, \cc commands.

\documentclass{book}
\usepackage{amsmath}

\newcommand{\RR}{\mathrm{R}}

\begin{document}

$ \RR$

\end{document}

Answer 1

Here, I used, to demonstrate, the three-letter sequence, since many two-letter combos are already taken.

\documentclass{book}
\usepackage{amsmath,pgffor}
\foreach\i in{A,...,Z}{\expandafter\gdef\csname\i\i\i\expandafter\endcsname
  \expandafter{\expandafter\mathrm\expandafter{\i}}}
\begin{document}
$\RRR$

$\BBB$
\end{document}

For lower-case, an identical loop can be added with only the limits changed to \foreach\i in{a,...,z}.

Percusse provided a more arcane version of the definition, which is nonetheless illustrative:

\foreach\i in{A,...,Z}{  
  \begingroup\edef\temp{\endgroup\noexpand\gdef\csname\i\i\i\noexpand\endcsname{%
  \noexpand\mathrm{\i}}}\temp
}

Nonetheless, David's suggestion of \newcommand\R{\mathrm}, which requires a slightly different syntax, is a better approach overall. I did it this way just to show it could be done.

Answer 2

Rather than define lots of commands you can define a command with arguments eg

\newcommand\R{\mathrm}

which allows \R R, \R x or \R{P} etc.

Although to be honest I would not do that. Any reasonable TeX editor could have (and probably has already) keyboard shortcuts to add \mathrm so it's no harder to add and much easier for anyone reading your source to read. It's worth making aliases for semantic markup so

\newcommand\vector{\mathrm}
 ...  \vector{x}...

if you are setting vectors in roman, as that allows alternative notations without changing the markup, but just aliasing a font change to use as a font change doesn't really gain a lot.

Answer 3

Taking your comment into consideration, maybe all you need is to define a shortcut in texstudio that will automatically insert \mathrm for you (replace cmdR by your favourite but not yet taken combo).

Answer 4

And here is solution based on TeX primitives and plain TeX macros:

\newcount\tmpnum

\def\setRR #1-#2{\tmpnum=`#1
   \loop
      \begingroup\lccode`.=\tmpnum
      \lowercase{\endgroup \expandafter\def\csname..\endcsname{\mathrm{.}}}
      \ifnum\tmpnum<`#2 \advance\tmpnum by1 \repeat
}
\setRR A-Z \setRR a-z

%% test:

\show\RR \show\xx

\bye

Answer 5

A variation on the theme:

\documentclass{book}
\usepackage{amsmath,pgffor}

\begingroup
\def\makethiscommand#1{\expandafter\gdef\csname #1#1#1\endcsname{\mathrm{#1}}}
\foreach\i in{A,...,Z}{%
  \expandafter\makethiscommand\expandafter{\i}%
}
\endgroup

\begin{document}
$\RRR$ \texttt{\meaning\RRR}

$\BBB$ \texttt{\meaning\BBB}
\end{document}