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オブジェクト・モデリングにおける動的モデルは状態機械で記述するのが基本です。つまり状態機械はオブジェクト・モデリングの重要な構成要素の一つということです。
ScalaでObject-Functional Programming(OFP)を行う場合でも、要求・分析・設計の各アクティビティを経て作成されたオブジェクト・モデル内の状態機械をどのように実装していくのかという実装方式が論点になります。
普通のOOP流の実装はすでに議論しつくされていると思いますが、OFPにおけるFPでの実装方式については、これから整備されていくことになると思います。
注意が必要なのはクラウド・アプリケーション開発をターゲットにする場合、伝統的なFPというよりMonadic Programming(以下MP)を経てFunctional Reactive Programming(以下FRP)がゴールになるということです。
このためFRPとして利用可能な状態機械実装を探っておきたいところです。
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I have been doing quite a bit of domain modeling using functional programming mostly in Scala. And as it happens when you work on something for a long period of time you tend to identify more and more patterns that come up repeatedly within your implementations. You may ignore these as patterns the first time, get a feeling of mere coincidence the next time, but third time really gives you that aha! moment and you feel like documenting it as a design pattern. In course of my learnings I have started blogging on some of these patterns - you can find the earlier ones in the series in:
Debasish氏が反対しているもう一つの主張が状態と振る舞いを一つのクラスにまとめることでカプセル化が促進されるということである。その代わりに、ドメインの振る舞いをスタンドアローンな関数として構築することにより、DDDの原理に沿った形でドメインモデルをよりよくモジュール化し実現することができる、と考えている。そのとき、全てのドメインの振る舞いはアグリゲートを表すモジュールの中の関数としてモデル化される。
ドメイン駆動設計における関数型パターン
オブジェクト指向で関数型を束ねる
Tomoharu ASAMI 「Scalaプログラミング・マニアックス」 p. 43
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A Useful application of Closures in JavaScript
It's hard to believe that at this time last year, I knew little to nothing about JavaScript. Like any good neophyte, I started off reading Douglas Crockford's "The Good Parts", which is an excellent book except for the section on Closures. Closures are famously tricky to understand, so I tried extra hard. Even after slogging my way through every technical detail, I still wasn't sure if I was "getting it". Like, okay there's functional scoping, but so what?
So now I present to you a useful application of closures (inspired by this great article on Closures in Python):
Attaching data to a function
Let's pretend I'm the owner of a website called DaBomb.com. We sell headphones and snowboards.
1. To fetch a list of all the headphones on our site, I call:
params = { color: "all", maxPrice: null, inCartOnly: false }; $.get('www.dabomb.com/items/headphones', params, renderListView);
2. When a user changes their search criteria, I make another call:
params = { color: "black", maxPrice: 150, inCartOnly: false }; $.get('www.dabomb.com/items/headphones', params, renderListView);
3. When a user goes to their shopping cart, I make yet another call with the new callback:
params = { color: "black", maxPrice: 150, inCartOnly: true }; $.get('www.dabomb.com/items/headphones', params, renderShoppingcartView );
I am tired of seeing my API url clutter up my code. What can I do? I can use a closure to make a new function that knows my API url:
