Here is a moral equivalent in C#: public abstract class Maybe<T> { public abstract T Value { get; } public virtual string Failure =

Here is a moral equivalent in C#: public abstract class Maybe<T> { public abstract T Value { get; } public virtual string Failure => null; public SelectMany<U, V>(Func<T, Maybe<U>> f, Func<T, U, V> g) { var that = f(this.Value); if(that.Failure != null) return new Failed(that.Failure); return new Success(g(this.Value, that.Value)); } public sealed class Success : Maybe<T> { public override Value { get; } public Success(T value) => this.Value = value; } public sealed class Failed : Maybe<T> { public override Failure { get; } public override Value => throw new InvalidOperationException(); public Failed(string s) => this.Failure = s; } } Maybe<string> UpdateCustomerWithErrorHandling() { return from req in receiveRequest(); from v in validateRequest(req) from c in canicalizeEmail(req) from d in db.updateDbFromRequest(req) from e in smptServer.sendEmail(req.Email) select "OK"; }