if test for 1 not 11

Question

It may seem rather silly, but I can't find an answer for this question. (I've been looking for one for a while already).

Suppose I want to have a macro with a single parameter. When this parameter equals 1, I want the macro to append the singular form of a word to the parameter, otherwise use the plural form.

I have the following code:

\newcommand{\sth}[1]{\textbf{(#1 
\if1#1thing)\else things)\fi}}

It works fine for any parameter except when it is a number greater than 1 but starting with 1 (e. gr. 11).

I am aware \if compares two tokens which in this case are characters. I am also aware there are solutions that either assume #1 is always a number (e.g. using \ifnum) or use additional packages (like ifthen or pdftexcmds). I don't want to assume #1 is a number, because it seems cleaner to me, and I still wonder whether there is a core LaTeX solution to this (w/o using further packages).

Edit: the question is, is there a way of knowing if the argument is exactly '1' without assuming it is a number nor using additional packages?

Thanks in advance

Answer 1

Here is an \ifnum comparison that can handle non-numeric inputs. It does it by comparing 1 with 0#1. If #1 is a number, the \ifnum comparison works in the standard way, since the leading 0 does not affect the numerical value.

If #1 is not a number, then the \ifnum argument expansion stops after the 0 with a false comparison (having already printed out #1), and then prints out things.

\documentclass{article}
\newcommand{\sth}[1]{\textbf{(#1 \ifnum1=0#1\relax thing\else things\fi)}}
\begin{document}
\sth{1}  vs. \sth{2} vs. \sth{11} vs. \sth{no}
\end{document}

Answer 2

\pdfstrcmp of pdfTeX expands two token groups and compares them as strings. If they are equal, \pdfstrcmp expands to 0, which can be tested with \ifnum or \if:

\ifnum\pdfstrcmp{#1}{1}=0 % space ends the number zero here
  ...
\else
  ...
\fi

or

\if0\pdfstrcmp{#1}{1}%
  ...
\else
  ...
\fi

Package pdftexcmds' \pdf@strcmp hides the different names and methods of the different TeX engines (pdfTeX, XeTeX, LuaTeX). "Vanilla" TeX is not supported.

If #1 can contain fragile stuff, then the LaTeX way is a protected expansion, e.g.:

\protected@edef\param{#1}%
\def\one{1}%
\ifx\one\param
  ...
\else
  ...
\fi

Or if the argument should not be expanded at all:

\def\param{#1}%
\def\one{1}%
\ifx\param\one
  ...
\else
  ...
\fi

Answer 3

Tests using \if..\else..\fi can be outmaneuvred by using arguments that contain unbalanced \if.. or \or or \else or \fi.

The following test works without additional packages only by means of expansion without any \if-conditionals. Everything is done by means of delimited macro arguments.

Of course you cannot successfully apply test-macros on arguments that contain \outer tokens.

You can easily enhance the test to fork whether "1" or "2" or something else/emptiness.

Ulrich

%%-------------------------------------------------------------------------
%% Paraphernalia:
%%.........................................................................
\long\def\firstoftwo#1#2{#1}%
\long\def\secondoftwo#1#2{#2}%
%%-------------------------------------------------------------------------
%% Check whether argument is empty:
%%.........................................................................
%% \CheckWhetherNull{<Argument which is to be checked>}%
%%                  {<Tokens to be delivered in case that
%%                    argument which is to be checked is empty>}%
%%                  {<Tokens to be delivered in case that
%%                    argument which is to be checked is not empty>}%
\long\def\CheckWhetherNull#1{%
  \expandafter\secondoftwo\string{\expandafter\secondoftwo
  \expandafter{\expandafter{\string#1}\expandafter\secondoftwo
  \string}\expandafter\firstoftwo\expandafter{\expandafter
  \firstoftwo\expandafter\secondoftwo\expandafter}\string
  }\firstoftwo
}%
%%-------------------------------------------------------------------------
%% Check whether argument contains no exclamation-mark on top-brace-level:
%%.........................................................................
%% \CheckWhetherNoExclamationMark{<Argument which is to be checked>}%
%%                  {<Tokens to be delivered in case that
%%                    argument which is to be checked does not contain !>}%
%%                  {<Tokens to be delivered in case that
%%                    argument which is to be checked does contain !>}%
\long\def\RemoveToExclamationMark#1!{}%
\long\def\CheckWhetherNoExclamationMark#1{%
  \expandafter\CheckWhetherNull\expandafter{\RemoveToExclamationMark#1!}%
}%
%%-------------------------------------------------------------------------
%% \ForkDigitOne{<Argument to check>}
%%              {<tokens in case argument to check is a
%%                single 1-character token of catcode 12>}
%%              {<tokens in case argument to check is not a
%%                single 1-character token of catcode 12>}
%%.........................................................................
\long\def\AtForkDigitOne#1!!1!#2#3!!!!{#2}%
\long\def\ForkDigitOne#1#2#3{%
   \CheckWhetherNoExclamationMark{#1}{%
    \AtForkDigitOne
    !#1!1!{#3}%<-EMPTY
    !!#1!{#2}%
    !!1!{#3}%<-ELSE
    !!!!%
  }{#3}%<-ELSE
}%

\ForkDigitOne{1}{One}{Not One}

\ForkDigitOne{\fi}{One}{Not One}

\ForkDigitOne{111}{One}{Not One}

\ForkDigitOne{!ttt{}111!!}{One}{Not One}

\ForkDigitOne{}{One}{Not One}

\ForkDigitOne{w22e2e}{One}{Not One}

\ForkDigitOne{ }{One}{Not One}

\bye