How to remove consecutive vertical whitespace from commands

Question

I would like to be able to write macros that approximate the behaviour of CSS's margin.

For example consider the following:

\newcommand{\marginspace}[1]{
  % Defines some combinable margin
  % This is what I'd like to know how to do
  % A naive implementation would just be:
  % \par\vspace{#1}
}
\newcommand{\lorem}{
  \marginspace{\baselineskip}
  Lorem
  \marginspace{\baselineskip}
}
\newcommand{\ipsum}{
  \marginspace{\baselineskip}
  Ipsum
  \marginspace{\baselineskip}
}

So then this document:

Foo
\lorem
\ipsum
Bar

Would be rendered something like:

Foo
Lorem
Ipsum
Bar

A naive implementation of \marginspace would just be \par\vspace{#1}, but this puts an extra line between "Lorem" and "Ipsum", where I'd like them combined:

Foo
Lorem
Ipsum
Bar

Is there any way to get the white space to be ignored if there's already sufficient whitespace above?

score 3 · Accepted Answer · answered May 17 '21 at 15:00

3

I think you are looking for \addvspace rather than \vspace, but this might depend on what exactly you are going do to with this.

\documentclass{article}
\newcommand{\marginspace}[1]{%
  \par\addvspace{#1}%
}
\newcommand{\lorem}{%
  \marginspace{\baselineskip}%
  Lorem
  \marginspace{\baselineskip}%
}
\newcommand{\ipsum}{%
  \marginspace{\baselineskip}%
  Ipsum
  \marginspace{\baselineskip}%
}
\begin{document}
Foo
\lorem
\ipsum
Bar
\end{document}

answered May 17 '21 at 15:00

campa

31,130

Much better answer than mine. +1 – Steven B. Segletes May 17 '21 at 15:03
1

If anyone's curious about the horizontal equivalent: https://tex.stackexchange.com/questions/15413/horizontal-spacing-double-hspace-removal – Alec May 18 '21 at 06:48
Great link @Alec. Thanks! – Steven B. Segletes May 18 '21 at 08:53

score 2 · Answer 2 · answered May 17 '21 at 14:52

If your two macros work in tandem...that is to say, if \lorem knows what to keep an eye out for (in this case \ipsum), then \lorem can absorb a few arguments and test them for \ipsum.

\documentclass{article}
\newcommand{\marginspace}[1]{
  \par\vspace{#1}
}
\newcommand{\lorem}[2]{
  \marginspace{\baselineskip}
  Lorem
  \ifx\par#1
    \ifx\ipsum#2\else
      \marginspace{\baselineskip}
    \fi
  \else
    \ifx\ipsum#1\else
      \marginspace{\baselineskip}
    \fi
  \fi
  #1#2%
}
\newcommand{\ipsum}{
  \marginspace{\baselineskip}
  Ipsum
  \marginspace{\baselineskip}
}
\begin{document}
Foo
\lorem
baz
\ipsum
Bar
\hrulefill
Foo
\lorem
\ipsum
Bar
\hrulefill
Foo
\lorem
\ipsum
Bar
\end{document}

How to remove consecutive vertical whitespace from commands

2 Answers2