public static void WalkFunctionBody([NotNull] BaseNode node, [NotNull] IList <string> list)
 {
     if (node is BlockStatementNode block)
     {
         TopLevelLexicallyDeclaredNamesWalker.Walk(block.Body, list);
     }
 }
 public static void Walk([NotNull] ProgramNode program, [NotNull] IList <string> list)
 {
     TopLevelLexicallyDeclaredNamesWalker.Walk(program.Body, list);
 }