PromisesWithValues.cs

using UnityEngine;
using System.Collections;
using System;
using System.Collections.Generic;

/// <summary>
/// Gareth Williams - Lonewolfwilliams LTD
/// http://lww.io
/// </summary>
public class Promises : MonoBehaviour 
{
	// Use this for initialization
	IEnumerator Start () 
	{
		var result = new Promise((f,r)=>
		{
			Debug.Log("one");
			StartCoroutine(DelayBySecs(1, f, "first"));
		})
		.Then((f,r)=>
		{
			Debug.Log("two");
			StartCoroutine(DelayBySecs(1, r));
		})
		.Then((f,r)=>
		{
			Debug.Log("three");
			StartCoroutine(DelayBySecs(1, f, "third"));
		})
		.Resolve();

		while(result.m_pending) yield return null;
		for(int i=0; i<result.value.Length; i++) Debug.Log(result.value[i]);
	} 
	private IEnumerator DelayBySecs<T>(float secs, Action<T> cc, T x)
	{
		yield return new WaitForSeconds(secs);
		cc.Invoke(x);
	}
	private IEnumerator DelayBySecs(float secs, Action cc)
	{
		yield return new WaitForSeconds(secs);
		cc.Invoke();
	}
}
public class Promise
{
	public Promise m_prev;

	public bool m_pending;

	public Action<object> m_fulfill;
	public Action m_reject;

	//public ITuple value = new Tuple();
	public object[] value = new object[0];

	public Action<Action<object>, Action> m_resolution;
	public Promise(Action<Action<object>, Action> resolution)
	{
		m_pending 			= true;
		this.m_resolution 	= resolution;
	}
	public Promise Resolve()
	{
		Promise final = null;
		final = this.Then((f,r)=>
		{
			Debug.Log("done");
			final.m_pending = false;
		});

		Promise first = final.First();
		first.m_resolution.Invoke(first.m_fulfill, first.m_reject);

		return final;
	}
	public Promise First()
	{
		Promise first = this;
		while(first.m_prev != null) first = first.m_prev;
		return first;
	}
}
public static class Extensions
{
	public static Promise Then(this Promise prev, Action<Action<object>, Action> resolution)
	{
		Promise current = new Promise(resolution);
		prev.m_fulfill = (x) => 
		{
			prev.m_pending = false;

			List<object> concat = new List<object>(prev.value);
			concat.Add(x);
			current.value = concat.ToArray();
			foreach(var s in current.value) Debug.Log("->"+s);

			current.m_resolution.Invoke(current.m_fulfill, current.m_reject);
		};
		prev.m_reject = () =>
		{
			current.value = prev.value;
			Debug.LogError("promise rejected");
			current.m_resolution.Invoke(current.m_fulfill, current.m_reject);
		};

		//link list
		current.m_prev = prev;

		return current;
	}
}

Beautiful!