Breaking change: Result and Reader

Reader

The Reader monad now has more advanced error handling (which is also reflected in the code-gen that wraps the Reader monad).

This means Reader<Env, A>.Run(env) now returns ReaderResult<A> instead of TryOption<A>. I have also removed Filter and Where from Reader and instead you should use:

    from x in success
        ? Reader<Env, A>(successValue)
        : ReaderFail<Env, A>("Fail message")
   ...

Filter and Where would return a result in a Bottom state, which isn't ideal. Obviously if you need this functionality back then you can create the extension methods yourself to create a similar functionality:

public static Reader<Env, A> Where<Env, A>(this Reader<Env, A> ma, Func<A, bool> f) =>
    ma.Bind(a => f(a) ? Reader<Env, A>(a) : ReaderFail<Env, A>(BottomException.Default));

Fail states can be created using:

    ReaderFail<Env, A>(string message);
    ReaderFail<Env, A>(string message, Exception exception);
    ReaderFail<Env, A>(Exception exception);

ReaderResult

ReaderResult<A> has Match and IfNone (so replace previous usage of IfNoneOrFail with IfNone). It also has conversion methods: ToSeq(), ToList(), ToOption(), ToOptionUnsafe(), ToOptionAsync(), ToEither(), ToEither(Func<Error, L> f), ToEitherUnsafe(), ToEitherUnsafe(Func<Error, L> f), ToEitherAsync(), ToEitherAsync(Func<Error, L> f), ToTry(), ToTryAsync()

Error

To facilitate the better error handling I needed to add a new Error type. The chances of this clashing with user's code is large, so it has been put into a new namespace: LanguageExt.Common. It can hold a message, a status value int, and an Exception.

Result

It seems to me that Result, OptionalResult, and Error belong in the same namespace so Result and OptionalResult have been moved to LanguageExt.Common.

On the whole you shouldn't really see Error or Result, most of the time you'll just be doing member access - and so the need to include the LanguageExt.Common should be rare.