enum Expr{
    case Literal{
        case Int(value:bigint);
        case String(value:bytearray);

        var type: *Type;
    }

    case BinOp(op:Token, lhs: *Expr, rhs: *Expr);
    case UnOp(op:Token, arg: *Expr);

    var loc: SourceLocation;
    var meta: *MetadataNode;
}

void process_expr(e:*Expr){
    switch (e){
    case Literal.String(value):
        print("found some string!" + value.to_utf8() + " at " + e.loc);
    case BinOp(_, lhs, rhs):
        process_expr(lhs);
        process_expr(rhs);
    case UnOp(_, arg) as unop:
        process_expr(arg);
        work_with_unop(unop);
    }
}

void work_with_unop(unop:*UnOp){
    if (unop.op == Token.Plus) {
        unop.op = Token.Minus;
    }
}