gistfile1.cs

using System;

namespace LangExt.Playground
{
    public sealed class LazyVal<T>
    {
        T value;
        bool hasValue = false;
        readonly Func<T> f;

        public LazyVal(Func<T> f) { this.f = f; }

        public T Value
        {
            get
            {
                if (hasValue) return value;
                value = f();
                hasValue = true;
                return value;
            }
        }

        public static implicit operator T(LazyVal<T> v) { return v.value; }
        public static implicit operator LazyVal<T>(Func<T> f) { return new LazyVal<T>(f); }
        public static implicit operator LazyVal<T>(T x) { return new LazyVal<T>(() => x); }

        public LazyVal<U> Bind<U>(Func<T, LazyVal<U>> f)
        {
            return new LazyVal<U>(() => f(Value));
        }

        public U Map<U>(Func<T, U> f)
        {
            return new LazyVal<U>(() => f(Value));
        }

        public LazyVal<T> OrElse(LazyVal<T> v)
        {
            if (v.hasValue) return this;
            else return v;
        }
    }
}