How to remove space before or after argument then compare it with a string

Question

I have this MWE

\documentclass{article}

\def\posa(#1) {%
    \ifx #1+ Plus \else \ifx #1- Minus\else Retry \fi \fi
}   
\begin{document}

    \posa(+)

\end{document}

Which compare argument of \posa command with + and -, I need to remove space before and after argument of \posa so that even if we wrote:

\posa( +) or \posa(+ ) or \posa( + ) we get Plus as result (same with -)

Related: Trimming whitespace around text (like LTRIM, RTRIM and TRIM) — Werner, Aug 14 '17 at 14:16

score 2 · Answer 1 · answered Aug 14 '17 at 13:08

2

None of this is really latex, but since you are using def

\documentclass{article}

\def\posa#1#2#3{%
    \ifx +#2Plus\else \ifx-#2Minus\else Retry \fi\fi
}   
\begin{document}

    \posa(+)

    \posa( -)

    \posa(?)

    \posa( + )

\end{document}

Your original had a required space after the ) but I removed that requirement here.

Note that it is safer to use \ifx+#1 than \ifx#1+ for example in your original if you use \posa(zz) the first test \ifx #1+ would be true as it would test z and z.

answered Aug 14 '17 at 13:08

David Carlisle

757,742

How about argument #1 and #3 of \posa? – Salim Bou Aug 14 '17 at 13:48
If I try with \posa(zz) a parenthesis appear Retry ) – Salim Bou Aug 14 '17 at 13:52
@SalimBou #1 is ( and #3 is ) (you could check that and raise an error if not.) \ifx(#1\else \ERROR\fi ... – David Carlisle Aug 14 '17 at 13:54
@SalimBou why do you want the () in the arguments anyway? (which breaks all latex syntax guidelines) If you just had \def\posa#1{\ifx+#1.... and \posa{+} or \posa + it would be simpler. – David Carlisle Aug 14 '17 at 13:57

Steven B. Segletes · Accepted Answer · 2017-08-14T13:43:27.307

Here, I use a listofitems package \readlist* to read the argument as a 1-item list, with leading/trailing spaces stripped. Then I can do an \if (expanded) comparison on whether the list item is a + or -.

\documentclass{article}
\usepackage{listofitems}
\def\posa(#1){%
    \readlist*\myarg{#1}
    \if+\myarg[1]Plus\else \if-\myarg[1]Minus\else Retry \fi\fi
}   
\begin{document}

    \posa(+)

    \posa( -)

    \posa(?)

    \posa( + )

\end{document}

If one needs the test to be done with the non-expanded argument of \posa, then this would suffice, since \myarg[1], when twice expanded, yields the token(s) of the argument (leading/trailing spaces removed).

\documentclass{article}
\usepackage{listofitems}
\def\posa(#1){%
    \readlist*\myarg{#1}
    \expandafter\expandafter\expandafter\def\expandafter\expandafter\expandafter\tmp%
      \expandafter\expandafter\expandafter{\myarg[1]}%
    \expandafter\ifx\expandafter+\tmp Plus\else%
      \expandafter\ifx\expandafter-\tmp Minus\else Retry \fi\fi%
}   
\begin{document}

    \posa(+)

    \posa( -)

    \posa(?)

    \posa( + )

\end{document}

In plain TeX, use \input{listofitems} instead of \usepackage{listofitems}.

StefanH · Answer 3 · 2017-08-14T14:08:40.127

2

I am not sure I can explain why, but adding a second argument will suppress the spaces.

\documentclass{article}
\def\posa(#1#2){%
  \ifx+#1Plus\else\ifx-#1Minus\else Retry\fi\fi
}   
\begin{document}
    \posa(+)

    \posa( -)

    \posa(?)

    \posa( + )

    \posa(- )

    \posa(zz)
\end{document}

edited Aug 14 '17 at 14:08

answered Aug 14 '17 at 13:59

StefanH

13,823

score 2 · Answer 4 · answered Aug 14 '17 at 15:27

With xparse we have easier syntax:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand{\posa}{ r() }
 {
  \str_case_x:nnF { \tl_trim_spaces:n { #1 } }
   {
    {+}{Plus}
    {-}{Minus}
   }
   {Retry}
 }
\ExplSyntaxOff

\begin{document}

X\posa(+)X\posa( +)X\posa(+ )X\posa( + )X

X\posa(-)X\posa( -)X\posa(- )X\posa( - )X

X\posa(=)X\posa( =)X\posa(= )X\posa( = )X

\end{document}

How to remove space before or after argument then compare it with a string

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