If this expression parser is given an input file containing

a = b + c * d;

x = -y;

p = --q;

e = f + g + h + i;

j = k * l * m * n;

q = 3 + 4 * 5;

it will print

<n_expr_list
  <n_assign n_id[a]
    <n_plus n_id[b]
      <n_times n_id[c] n_id[d] >
    >
  >
  <n_assign n_id[x]
    <n_uminus n_id[y] >
  >
  <n_assign n_id[p]
    <n_uminus n_uminus n_id[q] >
  >
  <n_assign n_id[e]
    <n_plus
      <n_plus
        <n_plus n_id[f] n_id[g] > n_id[h]
      > n_id[i]
    >
  >
  <n_assign n_id[j]
    <n_times
      <n_times
        <n_times n_id[k] n_id[l] > n_id[m]
      > n_id[n]
    >
  >
  <n_assign n_id[q]
    <n_plus n_icon[3]
      <n_times n_icon[4] n_icon[5] >
    >
  >
>