scope jsonDecode

sO jsonDecode(S text) {

  ret new Y(text).parse();

}

// the miraculous class Y

sclass #Y {

  S text;

  LS tok;

  bool useOrderedMaps;

  int i = 1;

  *(S *text) {

    tok = jsonTok(text);

  }

  swappable RuntimeException fail(S msg) { ret main fail(msg); }

  O parse() {

    if (l(tok) == 1) null;

    ret parseExpr();

  }

  O parseExpr() {

    String t = tok.get(i);

    if (t.startsWith("\"") || t.startsWith("'")) {

      String s = unquote(tok.get(i));

      i += 2;

      return s;

    }

    if (t.equals("{"))

      return parseMap();

    if (t.equals("["))

      return this.parseList(); // avoid loading standard function "parseList"

    if (t.equals("null")) {

      i += 2; return null;

    }

    if (t.equals("false")) {

      i += 2; return false;

    }

    if (t.equals("true")) {

      i += 2; return true;

    }

    bool minus = false;

    if (t.equals("-")) {

      minus = true;

      i += 2;

      t = get(tok, i);

    }

    if (isInteger(t)) {

      int j = i;

      i += 2;

      if (eqOneOf(get(tok, i), ".", "e", "E")) {

        // rough parsing for doubles

        while (isInteger(get(tok, i))

          || eqOneOf(get(tok, i), ".", "e", "E", "-"))

          i += 2;

        double d = parseDouble(joinSubList(tok, j, i-1));

        if (minus) d = -d;

        ret d;

      } else {

        long l = parseLong(t);

        ret boxedIntOrLong(minus ? -l : l);

      }

    }

    fail("Unknown token " + (i+1) + ": " + t + ": " + text);

  }

  Object parseList() {

    consume("[");

    List list = new ArrayList;

    while (!tok.get(i).equals("]")) {

      list.add(parseExpr());

      if (tok.get(i).equals(",")) i += 2;

    }

    consume("]");

    return list;

  }

  Object parseMap() {

    consume("{");

    Map map = useOrderedMaps ? new LinkedHashMap : new TreeMap;

    while (!tok.get(i).equals("}")) {

      String key = unquote(tok.get(i));

      i += 2;

      consume(":");

      Object value = parseExpr();

      map.put(key, value);

      if (tok.get(i).equals(",")) i += 2;

    }

    consume("}");

    return map;

  }

  void consume(String s) {

    if (!tok.get(i).equals(s)) {

      S prevToken = i-2 >= 0 ? tok.get(i-2) : "";

      S nextTokens = join(tok.subList(i, Math.min(i+4, tok.size())));

      fail(quote(s) + " expected: " + prevToken + " " + nextTokens + " (" + i + "/" + tok.size() + ")");

    }

    i += 2;

  }

}