floruit.tex

\documentclass{article}

\usepackage{etoolbox}
\usepackage{zref}

\makeatletter

%% lifespan macros:

\newbool{fl_called}
\newcommand\fl@lifespan{}
\zref@newprop{lifespan}[]{\fl@lifespan}

\newcommand\fl@prefix{fl.~}
\newcommand\fl@infix{--}
\newcommand\fl@suffix{}

\newcommand\fl@handler[1]{%
	\ifnumcomp{#1}{<}{\fl@from}{\renewcommand\fl@from{#1}}{}%
	\ifnumcomp{#1}{>}{\fl@to}{\renewcommand\fl@to{#1}}{}%
}

\newcommand\floruitsave[1]{%
	\ifbool{fl_called}{%
		\newcommand\fl@from{10000}%
		\newcommand\fl@to{0}%
		\forlistloop{\fl@handler}{\fl@years}%
		\def\@fl{%
			\fl@prefix%
			\ifnumcomp{\fl@from}{=}{\fl@to}{\fl@to}{\fl@from\fl@infix\fl@to}%
			\fl@suffix%
		}%
		\renewcommand\fl@lifespan{\@fl}%
	}{}%
	\zref@labelbyprops{#1}{lifespan}%
}

\newcommand\floruitoutput[1]{%
	\zref@extract{#1}{lifespan}%
}

\newcommand\floruit[1]{#1\booltrue{fl_called}\listadd\fl@years{#1}}

\makeatother

%% person environment:

\newcounter{person}

\newenvironment{person}[1]{%
	\refstepcounter{person}%
	\textbf{\theperson:~#1} \textit{\floruitoutput{person:\theperson}}\par%
}{%
	\floruitsave{person:\theperson}%
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{document}

\begin{person}{Old MacDonald}
Old MacDonald had a farm in \floruit{1923}, but appears to have sold it by \floruit{1940}.
\end{person}

\begin{person}{Gary Cooper}
Gary Cooper starred in High Noon (\floruit{1952})...
\end{person}

\begin{person}{John Doe}
Blah blah (\floruit{1912}), more blah (\floruit{1930}) \& finally blah (\floruit{1931}).
\end{person}

\begin{person}{Jane Doe}
No floruit here...
\end{person}



The floruit should be with the name like so:

\textbf{3: John Doe} \textit{fl. 1912--1931}\par
Blah blah (1912), more blah (1930) \& finally blah (1931).\par

\end{document}

In my opinion this is very nice -- I did not think of writing the full lifespan to the .aux file via zref. This is possible of course, but it will bite you if you need the 'from' or 'to' value separately (just in case?)

I renamed it to lifespan as I intend to add \born{} and \died{} macros too, which if present will then override and be used instead of any \floruits.

But good point on saving from/to! It's still pretty early going for this project, so they might end up needed after all.