xkeyval: how to use default key value?

Question

I am trying to use the xkeyval package to include key arguments in a new environment. It seems to work except for default values. Here's my best try so far:

\documentclass{article}

\usepackage{xkeyval}


\makeatletter
\define@key{Mystuff}{foo}[what]{\def\foo{#1}}
\define@key{Mystuff}{bar}[whatever]{\def\bar{#1}}
\savekeys{Mystuff}{foo,bar}
\makeatother

\newenvironment{myenv}[1][]%
{\setkeys{Mystuff}{#1}BEGIN \foo}
{END \bar}

\begin{document}

\begin{myenv}[bar=BAAAR]
Uh?
\end{myenv}

\end{document}

But this will cause LaTeX to complain about \foo being undefined:

! Undefined control sequence.
\\myenv [#1]->\setkeys {Mystuff}{#1}BEGIN \foo 

l.18 \begin{myenv}[bar=BAAAR]

And the output will be something like "BEGIN Uh? END BAAAR" (without the default "what" value to \foo).

What am I doing wrong there, and how can I change this example so the default value for \foo will be used?

Answer 1

The default value is used when you specify the key, but don't assign a value: \begin{myenv}[foo] will define \foo to what. Say

\newenvironment{myenv}[1][]%
{\setkeys{Mystuff}{foo,bar,#1}BEGIN \foo}
{END \bar}

so that the default values will be applied.

Or say

\define@key{Mystuff}{foo}{\def\foo{#1}}
\define@key{Mystuff}{bar}{\def\bar{#1}}

and

\newenvironment{myenv}[1][]%
{\setkeys{Mystuff}{foo=what,bar=whatever,#1}BEGIN \foo}
{END \bar}

A key is never evaluated if it's not specified in \setkeys.

---

Actually, as pointed out by Ulrike Fischer and Ahmed Musa, one can "preset" some keys, and this will be equivalent to specify them in the \setkeys list:

\define@key{Mystuff}[what]{foo}{\def\foo{#1}}
\define@key{Mystuff}[whatever]{bar}{\def\bar{#1}}
\presetkeys{Mystuff}{foo,bar}{}

What strategy to employ depends mostly on the applications. If you always need that foo and bar are set, then \presetkeys is more economical, as the assignment wouldn't be performed twice when the key is specified.

The \presetkeys, however, can go also in the definition of the environment, so the definition of your environment can be

\newenvironment{myenv}[1][]%
  {\presetkeys{foo,bar}{}%
   \setkeys{Mystuff}{#1}BEGIN \foo}
  {END \bar}

and this wouldn't influence other environments using the Mystuff keys.

Answer 2

\savekeys is the wrong command. What you want is

\presetkeys{Mystuff}{foo,bar}{}

The key foo will then be inserted at the start of the \setkeys list.