Define a macro based on parameter

Question

I am trying to create a macro that creates two macros. The first sets a default value and the second creates a macro to redefine the first. I am trying to generalize a common pattern I am using quite a bit.

\newcommand{\mkMac}[1]{%
\newcommand{\the#1}{The macro ##1}
\newcommand{\#1}[1]{\renewcommand{\the#1}{##1}}
}

Usage:

\mkMac{affilation}
\affilation{University}
Welcome to \theaffilation

I added context. I searched for a similar question, but I couldn't find it. — Ra is dead, Sep 03 '13 at 14:56
This may be relevant: http://tex.stackexchange.com/questions/109615/best-practice-for-creating-user-defined-command-names — Steven B. Segletes, Sep 03 '13 at 15:45
\the syntax is used for LaTeX counter and lengths so you would better off with a different prefix. — percusse, Sep 03 '13 at 15:49

score 8 · Accepted Answer · answered Sep 03 '13 at 16:27

With \newcommand and \renewcommand you have to use \csname...\endcsname, with some \expandafter to build the control sequence before \newcommand or \renewcommand comes into action:

\newcommand{\mkMac}[1]{%
  \expandafter\newcommand\csname the#1\endcsname{%
    Call the macro \texttt{\expandafter\string\csname #1\endcsname}!%
  }%
  \expandafter\newcommand\csname #1\endcsname[1]{%
    \expandafter\renewcommand\csname the#1\endcsname{##1}%
  }%
}

\mkMac{affiliation}
\show\theaffiliation
\show\affiliation
\affiliation{University}
\show\theaffiliation

\stop

This is the output on the terminal when running the example (\stop is just to end the run):

This is pdfTeX, Version 3.1415926-2.5-1.40.14 (TeX Live 2013)
 restricted \write18 enabled.
entering extended mode
(./mkmak.tex
LaTeX2e <2011/06/27>
Babel <3.9f> and hyphenation patterns for 78 languages loaded.
> \theaffiliation=\long macro:
->Call the macro \texttt {\expandafter \string \csname affiliation\endcsname }!.
l.11 \show\theaffiliation

?
> \affiliation=\long macro:
#1->\expandafter \renewcommand \csname theaffiliation\endcsname {#1}.
l.12 \show\affiliation

?
> \theaffiliation=\long macro:
->University.
l.14 \show\theaffiliation

?
 )
No pages of output.
Transcript written on mkmak.log.

So \mkMak{affiliation} defines a temporary value for \theaffiliation and the macro \affiliation; the call \affiliation{University} redefines \theaffiliation to University.

Tobi · Answer 2 · 2013-09-03T15:54:32.647

5

You can use etoolbox’ \csdef but in this case LaTeX won’t test if a macro is defined already.

\usepackage{etoolbox}
\newcommand{\mkMac}[1]{%
  \csdef{the#1}{The macro ##1}
  \csdef{#1}##1{\csdef{the#1}{##1}}
}

Note that with \csdef the braces around the macro name are mandatory and the leading backslash must be omitted.

edited Sep 03 '13 at 15:54

answered Sep 03 '13 at 15:33

Tobi

56,353

I think that \csdef{#1}##1{\csdef{#1}{##1}} should be \csdef{#1}##1{\csdef{the#1}{##1}} – Ra is dead Sep 03 '13 at 15:52
@Raisdead: You’re right. Didn’t test is since you din’t provide a MWE ;-) – Tobi Sep 03 '13 at 15:55

score 3 · Answer 3 · edited Jun 10 '20 at 12:32

If you don’t want to think about expansion and want to use the functions of \newcommand, you can use the macros \csnewcommand and \recsnewcommand defined as

\makeatletter
\newcommand*\csnewcommand{\@star@or@long\csnew@command}
\newcommand*\csnew@command[1]{\expandafter\new@command\csname#1\endcsname}
\newcommand*\recsnewcommand{\@star@or@long\recsnew@command}
\newcommand*\recsnew@command[1]{\expandafter\renew@command\csname#1\endcsname}
\makeatletter

This way you can use both the starred and un-starred version without \expandafter.

Code

\documentclass{article}
\makeatletter
\newcommand*\csnewcommand{\@star@or@long\csnew@command}
\newcommand*\csnew@command[1]{\expandafter\new@command\csname#1\endcsname}
\newcommand*\recsnewcommand{\@star@or@long\recsnew@command}
\newcommand*\recsnew@command[1]{\expandafter\renew@command\csname#1\endcsname}
\makeatletter
\newcommand{\mkMac}[1]{%
  \csnewcommand{the#1}{The macro #1}%
  \csnewcommand{#1}[1]{\recsnewcommand{the#1}{##1}}}
\begin{document}
\mkMac{affilation}
Welcome to ``\theaffilation''.
\affilation{University}
Welcome to ``\theaffilation''.
\end{document}

Output

Welcome to “The macro affilation”.

Welcome to “University”.

score 1 · Answer 4 · answered Nov 18 '14 at 09:46

1

The two-line solution which uses only TeX primitives follows:

\def\sdef#1{\expandafter\def\csname#1\endcsname}
\def\mkMac#1{\sdef{the#1}{The macro #1}\sdef{#1}##1{\sdef{the#1}{##1}}}

\mkMac{affilation}
\affilation{University}
Welcome to \theaffilation

answered Nov 18 '14 at 09:46

wipet

74,238

Without any control whatsoever about the macro already having a definition. – egreg Nov 18 '14 at 10:33
We are using TeX and this is normal behavior of TeX. The question doesn't include explicitly the task about this more intelligence. But if somebody needs this, then my macro would have three lines no two lines. That is all. – wipet Nov 19 '14 at 07:26

score 0 · Answer 5 · answered Nov 17 '14 at 20:31

LaTeX defines a short interface similar to that provided by etoolbox in the form of \@namedef (from latex.ltx):

\def\@namedef#1{\expandafter\def\csname #1\endcsname}

Here is a minimal example showing the usage:

enter image description here

\documentclass{article}

\makeatletter
\newcommand*{\mkMac}[1]{%
  \@namedef{the#1}{The macro #1}%
  \@namedef{#1}##1{\@namedef{the#1}{##1}}}
\makeatother

\begin{document}
\mkMac{affilation}
Welcome to ``\theaffilation''.

\affilation{University}
Welcome to ``\theaffilation''.
\end{document}

Without any control whatsoever about the macro already having a definition. This is essentially the same answer as Tobi's. — egreg, Nov 18 '14 at 10:33

Define a macro based on parameter

5 Answers5

Code

Output

Linked

Related