try {
env = water.cascade.Exec.exec(cascade._ast);
StringBuilder sb = env._sb;
if( sb.length()!=0 ) sb.append("\n");
if (env.isAry()) {
Frame fr = env.popAry();
cascade._key = fr._key;
cascade._num_rows = fr.numRows();
cascade._num_cols = fr.numCols();
cascade._col_names = fr.names();
cascade._string = null;