Chained null checks and the Maybe monad & others

ObjectExtensions

using System;

public static class ObjectExtensions
{
    public static TResult With<TInput, TResult>(this TInput o, Func<TInput, TResult> evaluator)
        where TResult : class
        where TInput : class
    {
        if (o == null) return null;
        return evaluator(o);
    }

    public static TResult Return<TInput, TResult>(this TInput o, Func<TInput, TResult> evaluator, TResult failureValue)
        where TInput : class
    {
        if (o == null) return failureValue;
        return evaluator(o);
    }

    public static TInput If<TInput>(this TInput o, Func<TInput, bool> evaluator)
        where TInput : class
    {
        if (o == null) return null;
        return evaluator(o) ? o : null;
    }

    public static TInput Unless<TInput>(this TInput o, Func<TInput, bool> evaluator)
        where TInput : class
    {
        if (o == null) return null;
        return evaluator(o) ? null : o;
    }

    public static TInput Do<TInput>(this TInput o, Action<TInput> action)
        where TInput : class
    {
        if (o == null) return null;
        action(o);
        return o;
    }
}