How to change CancellationToken in EnvIO?

[rvahitov]

Please excuse my bad English.
How to change EnvIO to use external CancellationToken? Here is a code example:

private static readonly Error InternalError = Error.New(500, "Something went wrong");
    public async Task<IResult> FindCompanyById(string id, CancellationToken cancellationToken)
    {
        var io =
            from entity in DB.FinCompanyById(id) 
                           | Prelude.@catch(IO<CompanyEntity>.Fail(InternalError))
            from dto in entity.MapToDto()
            select dto.ToHttpResult();

        var fin = await io.RunSafeAsync(); // <- How to pass EnvIO with method's CancellationToken
        return fin.IfFail(e => e.ToHttpResult());
    }

[louthy]

The EnvIO is optional:

public static ValueTask<Fin<A>> RunSafeAsync<A>(this K<IO, A> ma, EnvIO? envIO = null) =>
    ma.As().Try().Run().RunAsync(envIO);

So you can provide your own with your own CancellationToken:

using var envIO = EnvIO.New(cancellationToken);
var fin = await io.RunSafeAsync(envIO)

By the way, not sure if this just example code, but I would separate out your IO functionality:

public IO<CompanyDTO> FindCompanyById(string id) =>
    from entity in DB.FinCompanyById(id) 
                   | @catch(IO<CompanyEntity>.Fail(InternalError))
    from dto in entity.MapToDto()
    select dto;

And create an extension to do the 'messy stuff':

public static async Task<IResult> RunToHttp(this IO<A> io, CancellationToken token)
{
    using var envIO = EnvIO.New(token);
    var fin = await io.RunSafeAsync(envIO);
    return fin.IfFail(e => e.ToHttpResult());
}

Then you can use the IO returning methods directly in your web-handlers:

FindCompanyById(id).RunToHttp(token);

Which keeps the invocation behaviour separate from your lovely pure IO code. Which is good for separation of concerns, but it also means you can compose your FindCompanyById with other IO returning methods/functions :)

Also, use:

using static LanguageExt.Prelude; 

That means you don't need the Prelude. prefix on @catch.

[rvahitov]

Thank you very much for your detailed answer!