code: public Stream<VarSnippet> variables() {
          return snippets()
                       .filter(sn -> status(sn).isActive() && sn.kind() == Snippet.Kind.VAR)
                       .map(sn -> (VarSnippet) sn);
      }
docs: Returns the active variable snippets.
  This convenience method is equivalent to {@code snippets()} filtered for
  {@link jdk.jshell.Snippet.Status#isActive() status(snippet).isActive()}
  {@code && snippet.kind() == Kind.VARIABLE}
  and cast to {@code VarSnippet}.
  @return the active declared variables.