Automatic index entry for multiword terms

Question

I'm a lazy person. The less I type the better, so I'm trying to make a macro to automatically arrange index entries for multi-word terms (composed nouns actually).

Normally you'd have to type:

...some others exhibit \textbf{complex behaviour}\index{behaviour!complex}

I want to reduce it to

...some others exhibit \iterm{complex behaviour}

So I came out with the following macro [MWE]:

\documentclass{book}
\usepackage{xspace,xstring,imakeidx}
\makeindex

\newcommand{\iterm}[1]{%
    \def\myindex{#1}%
    \IfSubStr{#1}{ }{%
        \renewcommand{\myindex}{\StrBehind{#1}{ }!\StrBefore{#1}{ }}%
    }{}%
    #1\index{\myindex}\xspace%
}
\begin{document}

some others exhibit \iterm{behaviour!complex}
\printindex

\end{document}

There's also an optional argument in case I must force an entry, and later on I might add code to deal with prepositions (e.g. \iterm{world of LaTeX} → \index{LaTex!world of}, but its solution is a particular case of the one above.

So far I'm getting the following errors

• \renewcommand\myindex and \def\myindex:
  • Use of @index doesn't match its definition
  • Argument of @firstoftwo has an extra }.
• \edef\myindex and \protected\edef\myindex:
  • Use of @xs@IfSubStr@@ doesn't match its definition
  • Argument of @firstoftwo has an extra }.
  • Paragraph ended before @firstoftwo was complete.
  • Too many }'s.
• \protected\def\myindex and \DeclareRobustCommand:
  • Causes no error but does not add the entry to the index
• \let\myindex
  • Missing control sequence inserted.
  • Too many }'s.

I'm 100% sure this is doable but haven't figured out yet. Thanks in advance for your suggestions and answers.

Answer 1

You need to separate the splitting of the parts from the index making command.

\documentclass{book}
\usepackage{xstring,imakeidx}

\makeindex

\newcommand{\iterm}[1]{%
  #1%
  \IfSubStr{#1}{ }{%
    \StrBehind{#1}{ }[\secondword]%
    \StrBefore{#1}{ }[\firstword]%
    \index{\secondword!\firstword}%
  }{\index{#1}}%
}

\begin{document}

some others exhibit \iterm{complex behaviour}

Another \iterm{term}

And finish \iterm{z}

\printindex

\end{document}