我最近发现了FP错误(试图学习Haskell)，到目前为止，我对我所看到的(一流函数、惰性求值和所有其他好东西)印象深刻。我还不是专家，但我已经开始发现对基本算法进行“功能性”推理比命令式推理更容易(而且我很难回到我必须回到的地方)。
The one area where current FP seems to fall flat, however, is GUI programming. The Haskell approach seems to be to just wrap imperative GUI toolkits (such as GTK+ or wxWidgets) and to use "do" blocks to simulate an imperative style. I haven't used F#, but my understanding is that it does something similar using OOP with .NET classes. Obviously, there's a good reason for this--current GUI programming is all about IO and side effects, so purely functional programming isn't possible with most current frameworks.
My question is, is it possible to have a functional approach to GUI programming? I'm having trouble imagining what this would look like in practice. Does anyone know of any frameworks, experimental or otherwise, that try this sort of thing (or even any frameworks that are designed from the ground up for a functional language)? Or is the solution to just use a hybrid approach, with OOP for the GUI parts and FP for the logic? (I'm just asking out of curiosity--I'd love to think that FP is "the future," but GUI programming seems like a pretty large hole to fill.)
Windows Presentation Foundation证明了函数式方法非常适合GUI编程。它有许多功能方面，“好的”WPF代码(搜索MVVM模式)强调功能方法而不是命令式方法。我可以勇敢地宣称WPF是现实世界中最成功的功能GUI工具包:-)
WPF在XAML中描述了用户界面(尽管你也可以把它重写成函数式的c#或f#)，所以要创建一些用户界面，你可以这样写:
<!-- Declarative user interface in WPF and XAML -->
<Canvas Background="Black">
<Ellipse x:Name="greenEllipse" Width="75" Height="75"
Canvas.Left="0" Canvas.Top="0" Fill="LightGreen" />
</Canvas>
此外，WPF还允许你使用另一组声明性标记来声明性地描述动画和对事件的反应(同样，同样的事情也可以写成c# / f#代码):
<DoubleAnimation
Storyboard.TargetName="greenEllipse"
Storyboard.TargetProperty="(Canvas.Left)"
From="0.0" To="100.0" Duration="0:0:5" />
事实上，我认为WPF与Haskell的FRP有很多共同之处(尽管我相信WPF的设计者并不知道FRP，这有点不幸——如果你使用函数的观点，WPF有时会感觉有点奇怪和不清楚)。
Haskell方法似乎只是包装命令式GUI工具包(如GTK+或wxWidgets)，并使用“do”块来模拟命令式样式
这并不是真正的“Haskell方法”——这只是通过命令式接口最直接地绑定到命令式GUI工具包的方法。Haskell恰好有相当突出的绑定。
有几种比较成熟的，或者更具实验性的纯函数式/声明式gui方法，主要是在Haskell中，主要使用函数式响应式编程。
一些例子是:
reflex-platform, https://github.com/reflex-frp/reflex-platform
葡萄柚,http://hackage.haskell.org/package/grapefruit-ui-gtk
无功,http://hackage.haskell.org/package/reactive-glut
wxFruit, http://hackage.haskell.org/package/wxFruit
reactive-banana, http://hackage.haskell.org/package/reactive-banana
对于那些不熟悉Haskell、Flapjax、http://www.flapjax-lang.org/的人来说，http://www.flapjax-lang.org/是一个基于JavaScript的函数式响应式编程的实现。
