How to store multiple indexes state in smart contracts?

I’m struggling to store multiples index map inside my smart contract.

Here my code:

Edit: Found the issue, I needed to type my closure.

pub const BETLIST: Map<(&Addr, String), u8> = Map::new("votelist");

pub fn try_make_bet(deps: DepsMut, info: MessageInfo, bet: String) -> Result<Response, ContractError> {
    let api = deps.api;
    BETLIST.update(, (bet, &info.sender), |may_count| { Ok(may_count.unwrap_or_default() + 1) })?;
       .add_attribute("method", "try_make_bet"))

The console return the following error and I’m note sure how to solve it:

Also on Terra Discord, someone suggested to use IndexedMap for multiple indexes but the documentations is not very explicite and I did not find any example for IndexedMap usage.

Edit: Someone on Discord send me a more comprehensive guide

Thanks a lot !