how to choose only one situation by conditional cases

Question

environment:

\documentclass{beamer}

There is an idea that create a new CS, for example \modela like this:

\modela{enumerate}{#2}

would expand as follow:

\begin{frame}
     \begin{enumerate}
          #2
        \end{enumerate}
\end{frame}

while

\modela{description}{#2}

can be expanded as:

\begin{frame}
     \begin{description}
          #2
        \end{description}
\end{frame}

Any approach to fulfill this command by conditional command instead of the \if command sequence, because of not only two options? Thanks very mcuh!

Answer 1

Here's a simple version with kind of control over the input (it will only allow some specific environments instead of passing the environment name directly). You can add more cases (see interface3.pdf, page 39).

\documentclass{beamer}
\usepackage{expl3,xparse}

\ExplSyntaxOn
\tl_new:N \c_enum_tl
\tl_set:Nn \c_enum_tl {enumerate}
\tl_new:N \c_desc_tl
\tl_set:Nn \c_desc_tl {description}
\tl_new:N \l__hezilun_tmp_tl

\NewDocumentCommand{\modela}{m m}{
    \begin{frame}
    \tl_set:Nn \l__hezilun_tmp_tl {#1}
    \tl_case:Nn \l__hezilun_tmp_tl {
        \c_enum_tl {\begin{enumerate}#2\end{enumerate}}
        \c_desc_tl {\begin{description}#2\end{description}}
    }
    \end{frame}
}
\ExplSyntaxOff

\begin{document}
    \modela{enumerate}{
        \item Test
        \item Test
    }
    \modela{description}{
        \item[T] est
        \item[Test] Quack
    }
\end{document}

Update: If you want to have an error branch, just use

\tl_case:NnF \l__hezilun_tmp_tl {
    \c_enum_tl {\begin{enumerate}#2\end{enumerate}}
    \c_desc_tl {\begin{description}#2\end{description}}
}{Environment not allowed}

Answer 2

As mentioned in my comment (content of document is stolen from TeXnician answer):

\documentclass{beamer}
\newcommand{\modela}[2]{\begin{frame} \begin{#1}#2\end{#1} \end{frame} } 

\begin{document}
    \modela{enumerate}{
        \item Test
        \item Test
    }
    \modela{description}{
        \item[T] est
        \item[Test] Quack
    }
\end{document}