[Feature] Explore hiding async functions

[vicsn]

🚀 Feature

It might be possible to get rid of async function calls at the leo level. This needs a comprehensive security analysis before starting a PoC. We need to know whether we're not losing essential expressivity with regards to how developers can order their async calls to be executed.

For example, the following code:

mapping account: address => u64;

record token {
    owner: address,
    amount: u64,
}

async transition mint_public(
        public receiver: address,
        public amount: u64,
    ) -> (token, Future) {
        return (token {
            owner: receiver,
            amount,
        }, update_state(receiver, amount));
    }

    async function update_state(
        public receiver: address,
        public amount: u64,
    ) {
        let current_amount: u64 = Mapping::get_or_use(account, receiver, 0u64);
        Mapping::set(account, receiver, current_amount + amount);
   }

Could instead be represented as:

mapping account: address => u64;

record token {
    owner: address,
    amount: u64,
}

transition mint_public(
    public receiver: address,
    public amount: u64,
) -> token {
    let current_amount: u64 = Mapping::get_or_use(account, receiver, 0u64);
    Mapping::set(account, receiver, current_amount + amount);
    return token {
        owner: receiver,
        amount,
    };
}

[alexanderkim11]

This would be very nice from a readability perspective and for lowering the barrier to entry for newer Leo devs. Two questions/concerns off the top of my head:

1. I'm assuming that the async/Future model would still remain in place in Aleo instructions. In that case, what would be the steps for assigning operations to the off-chain vs on-chain portions? Would the compiler only assign mapping operations to the on-chain section and leave the rest off-chain?

2. There might some issues with loss of granularity in terms of users being able to choose exactly which operations execute on-chain vs off-chain. I can't think of any immediate reasons why this would be important, but it's probably worth asking