static S migrateClassesInStructureText(S s, O... migrations) {
  L<S> tok = javaTokForStructure(s);
  int n = l(tok);
  for (int i = 0; i < l(migrations); i += 2) {
    S from = cast migrations[i];
    S fromPlusDollar = from + "$";
    O to = migrations[i+1];
    S replacement = to instanceof S ? (S) to : dropPrefix("main$", className((Class) to);
    
    for (int i = 1; i < n; i += 2) {
      S t = tok.get(i)
      if (eq(t, from))
        tok.set(i, to);
      else if (startsWith(t, fromPlusDollar))
        tok.set(i, to + t.substring(l(from)));
    }
  }
  ret join(tok);
}

sS migrateClassesInStructureText(S s, MapSO migrations) {
  ret migrateClassesInStructureText(s, mapToParams(migrations));
}