Motoko Event Example

main.mo

actor {
    public type NotifyArgs = {
        callback : shared (Text) -> async ();
        transaction_id : Nat;
        metadata : Text;
    };

    public type TransferError = {
        #InsufficientBalance;
        #AmountTooLarge;
        #CallFailed;
        #Unknown;
    };

    public type TransferResult = {
        #Ok : Nat;
        #Err : TransferError
    };

    public type TransferRequest = {
        from : ?Principal;
        to : Principal;
        amount : Nat;
        notify : ?NotifyArgs;
    };

    public shared func transfer(transferRequest : TransferRequest) : async TransferResult {
        // Transfer logic above...
        switch (transferRequest.notify) {
            case (?v) {
                ignore v.callback(v.metadata);
            };
            case (null){};
        };
        return #Ok(0);
    };
};