multiple "else if"

Question

When labelling theorems and such, the label often takes this form :

\label{th:pyth}

So when referring to theorems, we often write :

According to theorem \ref{th:pyth} ...

But there is a little bit of redundancy with "theorem" and "th", so i wanted to create a command that would look like \refenv{th}{pyth} and that would output theorem 1. In order to do that, I would need to match the first argument to a string, so I tried this with the boolexpr package :

\usepackage{boolexpr}
\NewDocumentCommand{\refenv}{mm}{
    \switch
    \case{#1 = th} theorem
    \case{#1 = prop} proposition
    \case{#1 = coro} corollary
    \case{#1 = lem} lemma
    \case{#1 = prf} proof
    \case{#1 = def} definition
    \case{#1 = rem} remark
    \case{#1 = eq} equation
    \endswitch
    \ref{#1:#2}
}

Without success, since the boolexpr package only compares numbers. How can I find an equivalent that does not require multiple nested ifthenelse commands?

Answer 1

You might use a more flexible case switch function.

\documentclass{article}
\usepackage{amsthm}

\ExplSyntaxOn

\NewDocumentCommand{\refenv}{mm}
 {
  \str_case:nnF { #1 }
   {
    {th}{theorem}
    {prop}{proposition}
    {coro}{corollary}
    {lem}{lemma}
    {prf}{proof}
    {def}{definition}
    {rem}{remark}
    {eq}{equation}
   }
  {??}
  \nobreakspace\ref{#1:#2}
 }

\ExplSyntaxOff

% just a couple of envs
\newtheorem{theorem}{Theorem}
\theoremstyle{definition}
\newtheorem{definition}{Definition}

\begin{document}

\begin{definition}\label{def:important}
A \emph{definition} defines.
\end{definition}

\begin{theorem}\label{th:main}
The main theorem.
\end{theorem}

\begin{equation}\label{eq:best}
0=0
\end{equation}

We see that \refenv{th}{main} depends on \refenv{def}{important}
and \refenv{eq}{best}.

\end{document}

But it's better to use cleveref.

\documentclass{article}
\usepackage{amsthm}
\usepackage{cleveref}

% just a couple of envs
\newtheorem{theorem}{Theorem}
\theoremstyle{definition}
\newtheorem{definition}{Definition}

\begin{document}

\begin{definition}\label{def:important}
A \emph{definition} defines.
\end{definition}

\begin{theorem}\label{th:main}
The main theorem.
\end{theorem}

\begin{equation}\label{eq:best}
0=0
\end{equation}

We see that \cref{th:main} depends on \cref{def:important}
and \cref{eq:best}.

\end{document}

See the manual of cleveref to see how to customize the references.

Answer 2

The package cleveref, suggested by egreg, does everything I need, and does remove the redundancy, so no need to do else if shenanigans.