General ⇒ Wonky Behaivor from \@ifnextchar

[rspringuel]

When I compile the below MWE the first \@ifnextchar, always evaluates to false, which is clearly wrong in the last case. However, the second one (within \punctuationcheck) works just fine. Why would the same conditional evaluate to False and then True?

Code: Select all

\documentclass{article}

\makeatletter
\newcommand{\punctuationcheck}{%
	\@ifnextchar){I see a parens\relax}{%
	\@ifnextchar]{I see a square bracket\relax}{%
	\@ifnextchar.{I see a period\relax}{%
	\@ifnextchar,{I see a comma\relax}{I didn' t see anything\ }}}}%
}
\newcommand{\ie}{\textit{i.e.}\@ifnextchar,{I saw a comma\relax}{I didn't see a comma,}\punctuationcheck}
\makeatother

\begin{document}
\ie) test

\ie] test

\ie. test

\ie, test
\end{document}

What this produces when I compile it:

i.e.I didn’t see a comma,I see a parens) test
i.e.I didn’t see a comma,I see a square bracket] test
i.e.I didn’t see a comma,I see a period. test
i.e.I didn’t see a comma,I see a comma, test

[rspringuel]

Got an answer over on stackexchange. Turns out that the \@ifnextchar, within \ie was checking \punctuationcheck rather than the actual text. In order for it to look back at the actual text, I had to move \punctuationcheck inside the code tokens so that there was nothing after the three arguments to \@ifnextchar within \ie.

[Johannes_B]

If i had known, that you posted the question on Stackexchange, i would have checked if there are comments or anwsers already. Please avoid crossposting, or at least link the posts. Seems i have wasted some of my time. Please have a look at Gimme Pizza

Anyway, here is what i wrote up last night:



\@ifnextchar never got to see the comma, nor the period, nor the bracket and so on. What the command saw as the next char was \punctuationcheck.

What are you trying to achieve? We might find another solution.

Code: Select all

\documentclass{article}

\makeatletter
\newcommand{\punctuationcheck}{%
	\@ifnextchar){I saw a parens\relax}{%
	\@ifnextchar]{I saw a square bracket\relax}{%
		\@ifnextchar.{I saw a period\relax}{%
			\@ifnextchar,{I saw a comma\relax}{I didn' t see anything\
			}%
		}%
	}%
}%
}
\def\true{TRUE}
\def\false{FALSE}
\newcommand\ie{\@ifnextchar,{\true}{\false},}
\newcommand\ih{\@ifnextchar,{\true}{\false} }
\newcommand{\ig}{\textit{i.e.\space}\@ifnextchar,{I saw a comma\space\punctuationcheck}{I didn't see a comma,\space\punctuationcheck}}

\makeatother

\begin{document}
\ie) test \par
\ie] test \par
\ie. test \par
\ie, test \par\medskip
\ih) test \par
\ih] test \par
\ih. test \par
\ih, test \par\medskip
\ig) test \par
\ig] test \par
\ig. test \par
\ig, test \par

\end{document}