static ParseEnv parse_start(S input) {
  new ParseEnv env;
  env.ts = newThoughtSpace();
  try {
    env.ts.blockedA = litsymbolset("We", "Suggest");
    input = trim(input);
    env.input = input;
    print("Have input: " + input);
    post("We", "are parsing", quote(input));
    ret env;
  } on fail {
    env.close();
  }
}