```ebnf
code_block ::= '{' (inner_statements | top_statements) '}'
```
function(top) {
    const result = this.node("block");
    this.expect("{") && this.next();
    const body = top
      ? this.read_top_statements()
      : this.read_inner_statements();
    this.expect("}") && this.next();
    return result(null, body);
  }