Not enough material around using TryAsync and all the operators in general

[RollsChris]

Hi I'm struggling finding any good reading material on using this library.... I cant find anywhere that describes best ways to use TryAsync for example?

All the examples do not seem to be real world examples.. like making http calls, handling the results etc.

There are not many examples on chaining these operators together, to create functional chain with success and failure paths?

Thanks

[louthy]

Use Aff and Eff instead of TryAsync and Try. They're a more powerful superset of the functionality of Try* with a more opinionated approach to IO.

There's plenty of documentation here

Fundamentally though, Try* is just a monad like Option, IEnumerable, etc. They compose in the same way, and have the same core set of traits, like Map, Bind, Fold, ... and support in LINQ for composition. The only difference is that functions are lifted into the monad instead of values. So, if you know how to use one monad in this library, you pretty much know how to use them all.

   public Try<int> Foo() => 
       () => 100;

Is just a delegate:

Func<int>

TryAsync is the same, but with an async function

   public TryAsync<int> Foo() => async
       () => await Task.FromResult(100);

They both essentially represent a lazily evaluated union between Succ and Fail. Succ is the success state, which allows you to get at the bound value; Fail is the failure state which is an Exception. You can access those via Match, or they're handled automatically via bind.

[RollsChris]

Thanks for the reply. Of course i dint even look at the wiki :O sorry.

I have been using try Async like below:

await EnsureBrowserIsAvailable()
                .Match(
                    browserRevision => browserRevision,
                    e =>
                    {
                        AnsiConsole.MarkupLine("[red]ERROR FETCHING BROWSER[/]");
                        AnsiConsole.WriteException(e);
                        return Option<RevisionInfo>.None;
                    }
                )
                .BindAsync(browserRevision => EnsureBrowserIsLaunched()
                    .Match(
                        browser => browser,
                        e =>
                        {

                            AnsiConsole.MarkupLine("[red]ERROR LAUNCHING BROWSER[/]");
                            AnsiConsole.WriteException(e);
                            return Option<Browser>.None;
                        }
                    ).ToAsync()
                )
                .IfSomeAsync(async browser =>
                {
                    await TryAsync(browser.NewPageAsync())
                    .Match(page => page, e =>
                    {
                        AnsiConsole.MarkupLine("[red]ERROR OPENING NEW PAGE[/]");
                        AnsiConsole.WriteException(e);
                        return Option<Page>.None;
                    })
                    .ToAsync()
                    .IfSomeAsync(async page =>
                    {
                   ... DO WORK IF PIPE SUCESSFUL.....
                    });

Where EnsureBrowserIsAvailable is defined as:

 private static TryAsync<RevisionInfo> EnsureBrowserIsAvailable()
   {
       var browserFetcher = new BrowserFetcher();

       return TryAsync(browserFetcher
           .DownloadAsync());
   }

I want to switch to Aff, Could i possibly get some pointers?

I'm still struggling with understanding sorry, I'm hoping if you can see my current understanding you can tell me where I'm going wrong?
I feel like i really understand LINQ and everyone keeps telling me this is similar to LINQ but I'm not getting it.

Thanks for any help.

[louthy]

Lots of usage of Match is usually a red-flag. The reason is that you're manually trying to get the value out and deal with what the bind operation does automatically in monadic types.

I don't have access to all the types here, so I'll create some stub code so you can see a possible alternative approach.

First up, the logging you're doing isn't ideal, it's injecting side-effects without really capturing the common pattern. We'd prefer to put it into an Aff runtime (see the wiki docs to help here), but if you're not looking to go all-in on the Aff runtimes just yet, you could wrap them up like this:

    static AffCatch<A> CatchError<A>(string msg) =>
        @catch(e => true, LogError<A>(msg));
    
    static Func<Exception, Aff<A>> LogError<A>(string msg) =>
        exception =>
        {
            AnsiConsole.MarkupLine(msg);
            AnsiConsole.WriteException(e);
            return FailAff<A>(exception);
        };

CatchError will catch all exceptions (e => true) and then call LogError, which does your logging to AnsiConsole.

Next, I'll create a couple of dummy types to represent the Browser and Page:

    public record Browser
    {
        public Task<Page> NewPageAsync() =>
            Task.FromResult(new Page());
    }

    public record Page
    {
    }

Next, I'll wrap up the Ensure* and NewPage functions:

    static Aff<int> EnsureBrowserIsAvailable =>
        SuccessAff(0) | CatchError<int>("[red]ERROR FETCHING BROWSER[/]");

    static Aff<Browser> EnsureBrowserIsLaunched =>
        SuccessAff(new Browser()) | CatchError<Browser>("[red]ERROR LAUNCHING BROWSER[/]");
    
    static Aff<Page> NewPage(Browser browser) =>
        browser.NewPageAsync().ToAff() | CatchError<Page>("[red]ERROR OPENING NEW PAGE[/]");

Note how I use the | operator to catch any errors coming from the Aff (this is one feature that Try and TryAsync can't do). The SuccessAff calls are where you can inject your behaviours, you lift them into the Aff domain by replacing SuccessAff with Aff<T>(() => ...).

Now, I can replace your whole expression with something much more declarative and easier to use:

        from revision in EnsureBrowserIsAvailable
        from browser  in EnsureBrowserIsLaunched
        from page     in NewPage(browser)
        from work     in DoWorkWithPage(page)
        select work;

DoWorkWithPage is just a placeholder:

    static Aff<Unit> DoWorkWithPage(Page page) =>
        SuccessEff(unit);

You can invoke the Aff with await yourAff.Run() to get a Fin<A> out of the operation, that can be matched on. But you want to do that as little as possible, and stay inside the Aff if you can.

Finally, this looks to me like a UI automation project? If so, you might be interested in a project that my team have worked on that wraps Selenium in a less brittle functional interface - we use it for our automation testing.

[RollsChris]

Hey thanks so much. Thats cleared a lot up and is exactly what I'm trying to do ;) I love the sound of isotope80, I will try it out.

Love your work and you passion for programming. Much kudos to you.

[RollsChris]

Hey I have another question :)

I have this code I feel could be improved,...

 var accountLogic = from env in gotoMainPageLogic
                                   from accountsToLoop in SuccessAff(accounts)
                                   from _1 in LoopAccountsAndBattle(accountsToLoop, env.page, env.browser)
                                   select _1;

I would really like to do somthing like this:

 var accountLogic = from env in gotoMainPageLogic
                                   from accountsToLoop in SuccessAff(accounts)
                                   from account in accountsToLoop
                                   from _1 in Battle(page,ctx,table,account)
                                   select _1;

But accountsToLoop has left the Aff realm, not sure how I can put it back in and make a sequence.. if that makes sense?

LoopAccountsAndBattle looks like this:

  foreach (var account in accounts)
                          {
                              Aff<OutStandingBattle> startBattle = Battle(page, ctx, table, account);

                              var result = await startBattle.Run();
                          }

and Battle this:

  var userName = account.Name;
        var postingKey = account.Key;

        table.AddRow($"[green]{userName}[/]", $"", $"", $"", $"", $"", $"", $"", $"", "");
        ctx.Refresh();

        var rowIndex = table.Rows.Count - 1;

        var logInUser =
          from _ in MainDriverEnv.LogOut(page)
          from user in MainDriverEnv.Login(page, userName, postingKey)
          select user;

        var fetchGameSettings =
          from settings in MainDriverEnv.FetchGameSettings()
          select settings;

        var userDetails =
            from user in logInUser
            from settings in fetchGameSettings
            select (user: user, gameSettings: settings, questColor: MainDriverEnv.GetQuestColor(user, settings).IfNone(""));

        var startBattle =
           from user in userDetails
           from _1 in MainDriverEnv.DelayInput()
           from _2 in MainDriverEnv.Reload(page)
           from _3 in MainDriverEnv.DelayInput()
           from _4 in MainDriverEnv.CloseAllDialogs(page)
           from _5 in MainDriverEnv.DelayInput()
           from _6 in MainDriverEnv.ShowBattleHistory(page)
           from _7 in MainDriverEnv.DelayInput()
           from _8 in MainDriverEnv.CloseAllDialogs(page)
           from _9 in MainDriverEnv.DelayInput()
           from _10 in MainDriverEnv.ClickStartBattleButtonAsync(page)
           from outStandingBattle in MainDriverEnv.WaitForOutStandingBattle(page, userName, this.getOutstandingBattleQuery.Handle)
           from _11 in MainDriverEnv.ClickCreateTeamButtonAsync(page)
           from _12 in MainDriverEnv.UpdateTableRow(ctx, table, rowIndex, 1, new Markup($"[green]{outStandingBattle.Id}[/]"))
           from chosenTeam in MainDriverEnv.WaitForTeamToBeChosen(userName, user.questColor, (new GetBattleRecommendations()).GetRecommendation)
           from _13 in MainDriverEnv.UpdateTableRow(ctx, table, rowIndex, 2, new Markup($"[blue]{chosenTeam.SummonerName}[/]"))
           from _14 in MainDriverEnv.UpdateTableRow(ctx, table, rowIndex, 3, new Markup($"[blue]{chosenTeam.MonsterNames.ElementAtOrDefault(0)}[/]"))
           from _15 in MainDriverEnv.UpdateTableRow(ctx, table, rowIndex, 4, new Markup($"[blue]{chosenTeam.MonsterNames.ElementAtOrDefault(1)}[/]"))
           from _16 in MainDriverEnv.UpdateTableRow(ctx, table, rowIndex, 5, new Markup($"[blue]{chosenTeam.MonsterNames.ElementAtOrDefault(2)}[/]"))
           from _17 in MainDriverEnv.UpdateTableRow(ctx, table, rowIndex, 6, new Markup($"[blue]{chosenTeam.MonsterNames.ElementAtOrDefault(3)}[/]"))
           from _18 in MainDriverEnv.UpdateTableRow(ctx, table, rowIndex, 7, new Markup($"[blue]{chosenTeam.MonsterNames.ElementAtOrDefault(4)}[/]"))
           from _19 in MainDriverEnv.UpdateTableRow(ctx, table, rowIndex, 8, new Markup($"[blue]{chosenTeam.MonsterNames.ElementAtOrDefault(5)}[/]"))
           from _20 in MainDriverEnv.SelectCard(page, chosenTeam.SummonerId, chosenTeam.SummonerName)
           from _21 in MainDriverEnv.DelayInput()
           from _22 in MainDriverEnv.SelectMonsterCards(page, chosenTeam.MonsterIds, chosenTeam.MonsterNames)
           from _23 in MainDriverEnv.DelayInput()
           from _24 in MainDriverEnv.SubmitTeamAsync(page)
           from _25 in MainDriverEnv.DelayInput()
           from battleResult in MainDriverEnv.WaitForBattleResult(page, chosenTeam.BattleId, new GetBattleResultsQuery().Handle)
           from _26 in MainDriverEnv.UpdateTableRow(ctx, table, rowIndex, 9, new Markup(battleResult.Winner == userName ? $"[green]{battleResult.Winner}[/]" : $"[red]{battleResult.Winner}[/]"))
           select outStandingBattle;
        return startBattle;

As you can see i end up calling run twice...and one from inside the other. I know this is bad which is why I think there must be a better way.
I have been looking at Fold but it doesn't roll them up .. it just basically runs the last account :(
Any advice would be appreciated

[RollsChris]

I have ended up with something like this so a bit better:

var gotoMainPageLogic =
                            from revision in MainDriverEnv.EnsureBrowserIsAvailable
                            from browser in MainDriverEnv.EnsureBrowserIsLaunched
                            from page in MainDriverEnv.NewPage(browser)
                            from _1 in MainDriverEnv.Goto(page, SplinterLandsAPIURLS.MainURL)
                            select (page, browser);

                        var logic =
                            from env in gotoMainPageLogic
                            from _1 in Aff(async () =>
                            {
                                foreach (var account in accounts)
                                {
                                    table.AddRow($"[green]{account.Name}[/]", $"", $"", $"", $"", $"", $"", $"", $"", "");
                                    ctx.Refresh();
                                    Aff<OutStandingBattle> startBattle = Battle(env.page, ctx, table, account);
                                    var result = await startBattle.Run();
                                }

                                await env.browser.DisposeAsync();
                                return unit;
                            })
                            select _1;

                        var result = await logic.Run();