Aff: Problems with type inference

[dirkil]

Hi there,

I am currently collecting experience with programming with side effects and hence with Eff and Aff. I think I am getting the general idea but nevertheless I am struggling and some specific points and would be more than happy if someone could point me in the right direction.

Problem #1:
I have assembled a little example that shows my point. I have a Processor class that receives a List<Customer> which it should process and sends the result afterwards. Each action can obviously fail. Since the result for each customer is sent to someone, there is no overall result of the Start method except when there was a failure. So basically the structure is like that:

public Aff<IEnumerable<Unit>> Start(List<Customer> customers)
{
        return customers.Map(cust =>
                from _1 in LogInformation($"Processing {cust.Name}")
                from result in ProcessCustomer(cust)
                from _2 in SendResult(result)
                select unit)
            .Sequence();
}

Aff<Unit> LogInformation(string msg){}

Aff<ProcessResult> ProcessCustomer(Customer customer){}

Aff<Unit> SendResult(ProcessResult result){}

Unfortunately, the compiler gives me an error telling me that for the Sequence call the types cannot be inferred. I tried a few things but I cannot get it to work. So, if someone sees the problem I would be more than happy to be enlightened.

Problem #2:

The ProcessCustomer method has to deal with an Option<string> and also here the compiler does not like what I am doing. It says Arguments mismatch but I cannot see where it goes wrong.

public class Processor
{    
    
    private Aff<ProcessResult> ProcessCustomer(Customer customer)
    {
        return
            from inputFile in LoadInputFile(customer.Id)
            from result in inputFile.Match(     // <- Here it goes wrong
                Succ: file => ProcessFile(file), 
                None: _ => NoFileFound(customer)
                )
            select result;
    }

    private Aff<ProcessResult> ProcessFile(string file) =>
        from _1 in LogInformation($"Process {file}")
        select new ProcessResult();

    private Aff<ProcessResult> NoFileFound(Customer customer) =>
        from _1 in LogInformation($"No file found for {customer.Name}")
        select new ProcessResult();

    private Aff<Option<string>> LoadInputFile(int id)
    {
        return default;
    }
    
    private Aff<Unit> LogInformation(string msg) => 
        Aff<Unit>(() => default);   // Log Info somehow...
}

public class ProcessResult
{
    public string Description { get; set; } = string.Empty;
}

public class Customer
{
    public int Id { get; set; }
    
    
    public string Name { get; set; }
}

So, if someone could help me to get this compiled I would really appreciate it.

[harrhp]

1. There is no Sequence overload for IEnumerable<Aff<T>>. Use SequenceSerial or SequenceParallel
2. First argument's name of Option.Match is Some not Succ

[dirkil]

Thank you harrhp,

your answer was spot on. Thank you for pointing me out to SequenceSerial and SequenceParallel.

I can't believe that I used Succ instead of Some. Kind of embarassing... ;)