LangageExt: Chaining of two Eithers with Bind(), but cannot figure out how to use them to create another Either

Question

I am using LanguageExt to have functional programming features in C#. I have a method in which I want to build an instance of VaultSharp to access our HashiCorp Vault service. My goal is to create an instance of VaultClientSettings (see methods below) through a chain of two Eithers. In the end, either return an exception from any Either in the chain or the instance of VaultClientSettings. I think that I am close but cannot make the last step work. I'd appreciate your suggestions.

Here are links to the FP library for C# and the VaultSharp library;

Here is an image showing the error that I am seeing:

            Either<Exception, Uri> GetVaultUri() =>
                EnvironmentVariable.GetEnvironmentVariable(KVaultAddressEnvironmentVariableName)
                    .Map(uri => new Uri(uri));

            Either<Exception, TokenAuthMethodInfo> GetAuthInfo() =>
                EnvironmentVariable.GetEnvironmentVariable(KVaultTokenEnvironmentVariableName)
                    .Map(token => new TokenAuthMethodInfo(token));

            Either<Exception, VaultClientSettings> GetVaultClientSettings(
                Either<Exception, Uri> vaultUri,
                Either<Exception, TokenAuthMethodInfo> authInfo
            )
            {
                /////////////////////////////////////////////////////////////////////////
                // I have access to the uri as u and the authmethod as a, but I cannot //
                // figure out how to create the instance of VaultClientSettings.       //
                Either<Exception, VaultClientSettings>  settings =
                    vaultUri.Bind<Uri>(u =>
                        authInfo.Bind<TokenAuthMethodInfo>(a =>
                        {
                            Either<Exception, VaultClientSettings> vaultClientSettings = 
                                              new VaultClientSettings(u.AbsoluteUri, a);

                            return vaultClientSettings;
                        }));
            }

score 5 · Answer 1 · answered Jul 15 '20 at 09:31

As @hayden already noted: bind type argument was wrong (needs to be "right" type of result either type).

For LanguageExt: You can even omit the type argument if you return the correct type:

Either<Exception, VaultClientSettings>  settings =
                    vaultUri.Bind(u =>
                        authInfo.Bind(a =>
                        {
                            Either<Exception, VaultClientSettings> vaultClientSettings = 
                                              new VaultClientSettings(u.AbsoluteUri, a);

                            return vaultClientSettings;
                        }));

There is another form for this code (LINQ) which may be more readable to you:

var settings = from u in vaultUri
               from a in authInfo
               select new VaultClientSettings(u.AbsoluteUri, a);

Essentially Bind is SelectMany (from ...)

score 1 · Accepted Answer · answered Jul 15 '20 at 06:45

Haven't used either library, but looking at the signature for Bind:

Either<L, B> Bind<B>(Func<R, Either<L, B>> f)

Judging by the signature, the following should be valid:

Either<Exception, VaultClientSettings>  settings =
    vaultUri.Bind<VaultClientSettings>(u =>
        authInfo.Bind<VaultClientSettings>(a =>
        {
            Either<Exception, VaultClientSettings> vaultClientSettings = new VaultClientSettings(u.AbsoluteUri, a);

            return vaultClientSettings;
        }));

It was very helpful to see how you reasoned your way to making the code work! Thank you very much for your help! — A Bit of Help, Jul 15 '20 at 22:43

LangageExt: Chaining of two Eithers with Bind(), but cannot figure out how to use them to create another Either

2 Answers2