# Why is \prevgraf zero at the end of the paragraph (or even in the middle of the paragraph)?

Both \the\prevgraf show zero. I expected it to show current line counter.

\documentclass[varwidth]{standalone}
\usepackage{expl3}
\begin{document}
\parbox{40mm}
{ \parshape 3 0mm 40mm 5mm 35mm 10mm 30mm
This is sentence 1. This is sentence 2.
\the\prevgraf
This is sentence 3. This is sentence 4.
\par
}
\the\prevgraf
\end{document}


## 1 Answer

TeX cannot know the number of already typeset lines, when in the middle of a paragraph, for the simple reason it has not yet typeset it.

When a paragraph starts up, the value of \prevgraf is reset to 0; it is updated only when a paragraph or a “paragraph-so-far” has been split into lines (the latter case happens when a paragraph is interrupted by a displayed equation).

After a displayed equation is typeset, the value of \prevgraf is updated adding 3 to the value it was assigned when typesetting the “paragraph-so-far”.

Why does your last command show 0 as well? Because the paragraph was typeset in a group (the \parbox) and so the value of \prevgraf is forgotten as soon as the group ends.

\documentclass{article}

\begin{document}

\parbox{40mm}
{ \parshape 3 0mm 40mm 5mm 35mm 10mm 30mm
This is sentence 1. This is sentence 2.
$a=b$
\the\prevgraf
This is sentence 3. This is sentence 4.
\par
\the\prevgraf
}
\end{document}