Type forwarding is not recursive

[ptal]

This program is refused by the typing analysis by an error "inlining cycle detected":

grammar! neg_expr {

  factor
    = integer
    / unary_arith_expr

  unary_arith_expr
    = "+" factor
    / "-" factor > make_neg_expr

  integer
    = ["0-9"]+ > make_integer

  enum Expr {
    Number(u64),
    NegExpr(PExpr)
  }

  type PExpr = Box<Expr>;

  fn make_integer(raw_number: Vec<char>) -> PExpr {
    match u64::from_str(&*to_string(raw_number)).ok() {
      Some(x) => Box::new(Expr::number(x)),
      None => panic!("int literal is too large")
    }
  }

  fn make_neg_expr(expr: PExpr) -> PExpr {
    Box::new(Expr::NegExpr(expr))
  }
}

The type is not recursive because it just forwards the value and does not create new value during the recursive call.