whenenv.sty

% whenenv.sty - Conditional Environments using etoolbox

\RequirePackage{etoolbox}
\RequirePackage{environ}

% Internal marker to check if an environment has already been defined
\newcommand{\@whenenv@defined}[1]{\csdef{whenenv@#1@defined}{1}}
\newcommand{\@whenenv@isdefined}[1]{\csdef{whenenv@#1@checked}{\csuse{whenenv@#1@defined}}}
\newcommand{\@whenenv@checkdefined}[1]{%
  \ifcsdef{whenenv@#1@defined}{}{\PackageError{whenenv}{Environment `#1' has not been declared using \string\whenEnv}{You must use \string\whenEnv{#1} before \string\whenEnable or \string\whenDisable.}}
}

% \\whenEnv{name} -- defines a new toggle and environment, idempotent
\newcommand{\whenEnv}[1]{%
  \ifcsundef{whenenv@#1@defined}{%
    \newtoggle{when#1@toggle}%
    \@whenenv@defined{#1}%
    \NewEnviron{#1}{\iftoggle{when#1@toggle}{\BODY}{}}%
  }{}%
}

% \\whenEnable{name} -- enables the environment
\newcommand{\whenEnable}[1]{%
  \@whenenv@checkdefined{#1}%
  \toggletrue{when#1@toggle}%
}

% \\whenDisable{name} -- disables the environment
\newcommand{\whenDisable}[1]{%
  \@whenenv@checkdefined{#1}%
  \togglefalse{when#1@toggle}%
}