So, to answer my own question, for Template::Toolkit, this is a good way to do what I wanted in Template::Toolkit — though you're still free to suggest improvements :):

// BEGIN
[% IF list -%]
switch(x) {
[% FOREACH item IN list -%]
  case [% item %]:
    // code for [% item %]
[% UNLESS loop.last -%]
    break;
[% END -%]
[% END -%]
}
[% END -%]
// END
[download]

Run together with the following code:

#! perl -w
use Template;
my $tt = Template->new();
foreach my $data ([undef => undef], [ empty => []],
  ['("foo", "bar", "baz")' => [qw(foo bar baz)]]) {
    print "// List is $data->[0]:\n";
    $tt->process('tt2.tmpl', { list => $data->[1] });
    print "\n\n";
}
[download]

// List is undef:
// BEGIN
// END


// List is empty:
// BEGIN
switch(x) {
}
// END


// List is ("foo", "bar", "baz"):
// BEGIN
switch(x) {
  case foo:
    // code for foo
    break;
  case bar:
    // code for bar
    break;
  case baz:
    // code for baz
}
// END
[download]

Oh, and I feel that I had to tweak it quite a bit just to get the proper amount of whitespace, adding the hyphens just at the right spots (those -%] thingies). Either I'm missing something, or Template::Toolkit could use a touchup.

I'd also like to indent the loop control directives, without that the added leading whitespace shows up in the output. Can it be done? It seems like I have to choose between stripping all whitespace (including newlines) just in front or right after the directives, or no stripping at all. Can't I strip leading whitespace just up to, but excluding, the newline?