When is it better to use \par than \endgraf?

Question

Just yesterday I had to patch a package file (changing the description to indicate that the file had changed) to replace some \par to \endgraf because the code had bad interactions with non-\long macros.

When writing a package, are there cases where it is better to use \par than \endgraf?

Answer 1

It depends whether the commands you are defining are ever going to be executed at a place where \par doesn't mean \endgraf. For example latex.ltx has

  \let\tabularnewline\\%
    \let\par\@empty

so if you might want to be evaluated in the scope of those definitions you have to decide whether you want the current definition of \par or of \endgraf.

Answer 2

I would approach the answer to the question a bit differently (though it is essentially equiv to what David said):

• \par in LaTeX is equivalent to an empty line in the user document! Whatever the LaTeX gives as meaning to the "empty line" in a certain context is what \par would result to. Example given by David: in a tabular empty lines are ignored. But other usages are possible too.
• \endgraf in contrast is the primitive that "ends horizontal mode and breaks the material into lines given current parameters (or generates an error in places or does nothing if already in vertical mode ... add remaining subclasses of he primitive behavior here ...)".

In most cases \par runs the primitive behind \endgraf but not in all; sometimes it does additional things or other things.

So use \endgraf when you want to run the primitive and \par whenever you want the action that the user get (in current context) that is documented as the behavior of an empty line.

Answer 3

in many places, latex defines \par (usually via \everypar) to do a lot of non-obvious things, things which most ordinary users (and even some "experts") haven't investigated and aren't aware of. using \endgraf in these situations can lead to unexpected results.

some places where \par is much safer are

• for multiple paragraphs within one \item in a list

• at the end of a paragraph delimited (grouped) in braces

note that a blank line in these contexts is equivalent to \par, not \endgraf.

in certain situations, such as within a footnote in plain tex, \par isn't accepted, and \endgraf must be used instead. however, latex.ltx contains the line \let\endgraf=\par so i'm not really sure where \endgraf would be required in latex. (i've been corrupted sufficiently by long years of using plain tex that i sometimes get these things confused.)