Environment that counts words inside

Question

How can I create the environment that could count words inside itself? More specifically, I want to write an enviroment called "assignment" such that the code

\begin{assignment}
Some words here.
\end{assignment}

will result in "Some words here." in the text and, say, "3 words" in a margin paragraph.

I tried searching for that, but found only (external) tools to count words in the entire document, while I need to do this with LaTeX code and for a single environment (possibly repeated several times in a document).

Answer 1

How about counting white spaces? This seems easier to implement.

Here is a simple implement. You can improve it to deal with more complex texts.

\documentclass{article}
\begingroup
\lccode`\~=`\ %
\lowercase{%
  \gdef\assignment{\setcounter{word}{0}%
    \catcode`~=\active
    \def~{\space\stepcounter{word}}}}%
\endgroup
\newcounter{word}
\def\endassignment{\stepcounter{word}%
  \marginpar{\arabic{word} words}}
\begin{document}

\begin{assignment}
Here are some words.
\end{assignment}

\end{document}

Answer 2

Here's an environment that counts word inside. It uses the xesearch package, so it requires XeLaTeX.

Searching is kept local to the environment, that's why it's defined inside.

\documentclass{article}
\usepackage{xesearch}
\newcounter{words}
\newenvironment{assignment}{%
  \setcounter{words}{0}
  \SearchList!{wordcount}{\stepcounter{words}}
    {a?,b?,c?,d?,e?,f?,g?,h?,i?,j?,k?,l?,m?,
    n?,o?,p?,q?,r?,s?,t?,u?,v?,w?,x?,y?,z?}
  \UndoBoundary{'}
  \SearchOrder{p;}}{%
  \StopSearching
  \marginpar{\arabic{words} words}}
\begin{document}
\begin{assignment}
Here are a few words for a word count demonstration.
\end{assignment}
\end{document}