reads a simple inner statement
```ebnf
inner_statement ::= '{' inner_statements '}' | token
```
function() {
    switch (this.token) {
      case this.tok.T_FUNCTION:
        return this.read_function(false, false);
      // optional flags
      case this.tok.T_ABSTRACT:
      case this.tok.T_FINAL:
      case this.tok.T_CLASS:
        return this.read_class();
      case this.tok.T_INTERFACE:
        return this.read_interface();
      case this.tok.T_TRAIT:
        return this.read_trait();
      case this.tok.T_HALT_COMPILER: {
        this.raiseError(
          "__HALT_COMPILER() can only be used from the outermost scope"
        );
        // fallback : returns a node but does not stop the parsing
        let node = this.node("halt");
        this.next().expect("(") && this.next();
        this.expect(")") && this.next();
        node = node(this.lexer._input.substring(this.lexer.offset));
        this.expect(";") && this.next();
        return node;
      }
      default:
        return this.read_statement();
    }
  }