Is functional GUI programming possible?
I've recently caught the FP bug (trying to learn Haskell), and I've been really impressed with what I've seen so far (first-class functions, lazy evaluation, and all the other goodies). I'm no expert yet, but I've already begun to find it easier to reason "functionally" than imperatively for basic algorithms (and I'm having trouble going back where I have to).
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.)
Answer
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
That's not really the "Haskell approach" -- that's just how you bind to imperative GUI toolkits most directly -- via an imperative interface. Haskell just happens to have fairly prominent bindings.
There are several moderately mature, or more experimental purely functional/declarative approaches to GUIs, mostly in Haskell, and primarily using functional reactive programming.
Some examples are:
- reflex-platform, https://github.com/reflex-frp/reflex-platform
- grapefruit, http://hackage.haskell.org/package/grapefruit-ui-gtk
- reactive, http://hackage.haskell.org/package/reactive-glut
- wxFruit, http://hackage.haskell.org/package/wxFruit
- reactive-banana, http://hackage.haskell.org/package/reactive-banana
For those of you not familiar with Haskell, Flapjax, http://www.flapjax-lang.org/ is an implementation of functional reactive programming on top of JavaScript.