F# Console app is completely bombing out ignoring error handling - error-handling

Question

Excuse all the Console.WriteLines! Trying to figure out what is happening here.
The following code works if I run it in visual studio. When I compile and run it as a command line program - the line that tries to access an API using HttpClient completely stops the whole process and ends the program. No error handling, nothing. How can this happen? It bombs out if I remove the try/ with block as well. I am baffled.
let getTransactionData(ewayCSVData: EwayCSVData, httpClient: HttpClient) = task{
try
Console.WriteLine("get transaction data 1")
if ewayCSVData.transactionType.ToLower() = "refund" then
Console.WriteLine("get transaction data 2")
let url = "https://api.ewaypayments.com/Transaction/"+ewayCSVData.transactionNumber.ToString() + "/Refund"
Console.WriteLine("get transaction data 3")
let! postResult = httpClient.PostAsync(url, null)
Console.WriteLine("get transaction data 4")
let! result = postResult.Content.ReadAsStringAsync()
Console.WriteLine("get transaction data 5")
return result
else
Console.WriteLine("get transaction data 6")
let url: string = "https://api.ewaypayments.com/Transaction/"+ewayCSVData.transactionNumber
let! result = httpClient.GetStringAsync(url) // This line kills the whole process
Console.WriteLine("get transaction data 7")
return result
with (ex) ->
Console.Write(ex.Message)
Console.WriteLine("get transaction data 8")
return ""
}

Answer 1

I suspect your command-line program is simply exiting because it has reached the end of its code. You're launching an asynchronous task to access the API, but your program doesn't wait for this task to complete before exiting. That's why there are no exceptions or error messages.
To fix this, you can either explicitly wait on the result (e.g. via Task.Result), or put something at the end of your program to prevent the main thread from exiting. One common way to do this is by calling Console.ReadLine() on the last line of your top-level function.
For example, the following program (usually) exits without writing anything to the console:
open System
open System.Threading.Tasks
Task.Run<unit>(fun () ->
Console.WriteLine("Hello world"))
|> ignore
You can fix this by calling Result:
let task = Task.Run<unit>(fun () ->
Console.WriteLine("Hello world"))
task.Result
Or by calling Console.ReadLine:
Task.Run<unit>(fun () ->
Console.WriteLine("Hello world"))
|> ignore
Console.ReadLine() |> ignore
Note that my examples use Task.Run to illustrate the point. I don't think the F# task builder behaves quite the same way, but it sounds similar enough from your description.