http://www.altdevblogaday.com/2012/04/26/functional-programm...
He's a great developer and has always pushed boundaries. I look forward to his postmortem after this project is finished.
And yes, I'd love it if the compiler (or other static code analysis) could detect how pure various bits of code are, and give reports. For far too long, compiler authors have treated compilers as a big opaque box that end users (developers) submit code to, and the compiler hands out code as if from on high. Smart developers want to have a 2-way communication with their compiler, learning about all sorts of things -- functional purity, headers over-included, which functions it decided to inline or not (especially in LTCG), etc. It's not the 1960s anymore -- developers aren't bringing shoeboxes of punchcards of source code to submit for offline processing. Let's get closer to a coffee shop where we can talk in realtime.
In the immediate future, GHC is going to become more interactive by adding "type holes". Essentially, you can just leave out parts of your program and the compiler will tell you what type needs to go there. So instead of writing your program and checking if it typechecks, the type system can actually help you formulate the code in the first place!
Further afield, a bunch of people at the lab I'm working at are working on interactive systems that use a solver running in the background to solve problems for the programmers. These can be used to do all sorts of things from finding bugs to actually generating new code. Being interactive lets the solver suggest things without being 100% certain--the programmer can always supply more information. This also makes the solvers easier to scale because if it's not terminating quickly, it can just ask for more guidance from the programmer.
I think the general trend towards more interactive development is pretty exciting.
(For non- or fledgling Haskellers, "undefined" has any type, so if you define a function that plugs into your code and make its return value "undefined", then you can look at the type signature of the function and learn what the compiler proved about the type of that function. Pretty handy!)
However, it may be (if you'll pardon the expression) garbage collecting people that we don't know about, or cloning them in such a way that their multiple representations are indistinguishable.
This sounds like a game development reference that I'm missing. Can anyone explain?
[edit: If I'm wrong... ouch. But it's been a while.]
Games often want physics/model threads run with a consistent timestep, but have the rendering thread run as fast as possible.
This is a hugely successful pattern throughout a number of aspects of gaming, graphics being one of the most classic examples. Double-buffered graphics don't suffer as much from tearing and other display artifacts.
Not really, no. Immutability comes at the cost of performance compared to mutability. The gap is shrinking between the two, but it's still wide enough that using pure immutable structures for frame buffers, shaders and other graphical concepts is simply not an option to write games.
Haskell is interesting in the sense that it doesn't prevent you from using mutable structures (e.g. Lenses, Writer) but it encodes this information in the type system. I'm really curious to read the conclusions that Carmack will draw from his experience but I wouldn't be surprised to read that at the very low levels, mutable structures are just unavoidable for high performance games.
Also, mutable structures accessed by concurrent threads is a problem that's much less difficult than most people claim, and it's often much easier to reason about locks and semaphores than about immutable lazily initialized structures.
> using pure immutable structures for frame buffers, shaders and other graphical concepts is simply not an option to write games.
Seeing as people have written games in Haskell, this is clearly not true.
> Haskell is interesting in the sense that it doesn't prevent you from using mutable structures (e.g. Lenses, Writer)
Lenses and Writer both only use immutable data. It is possible to use actual mutable data in the ST and IO monads.
> but it encodes this information in the type system.
This is true of IO, but not of ST. With ST, runST :: (forall s. ST s a) -> a, hides the effects.
> it's often much easier to reason about locks and semaphores than about immutable lazily initialized structures.
I don't know what you mean by this. In terms of functional correctness, immutable data-strucutures, lazy or otherwise, are much easier to reason about. If you are talking about resource-usage, sure, it's a little harder to reason about lazy data-structures than strict ones, but give me a space leak over a race condition to track down any day.
Not really. There's no question whatsoever that GHC can run a fine Wolf3D on fractions of a modern hardware setup. You could do it in pure Python with no NumPy. There's tools to help with the laziness stuff and a 3D rendering loop will fit those perfectly.
But the performance limits of immutable structures for simulation and graphics are certainly interesting to me.
Not really, 3d rendering in haskell via opengl is not new or interesting at this point. Frag is 8 years old for example: http://www.haskell.org/haskellwiki/Frag
You can even stream textures asynchronously using PBOs (pixel buffer objects), and use dual PBOs like double buffers (or using copy-on-write techniques to only re-upload dirty rectangles...)
But it's nice to hear, hopefully John Carmack and id will make at least one more great in the future.
His games have been C++ for quite some time now.
And quite insulting.
Another factor is that the C code that comes out of id Software is just damn good. Go ahead and read the Quake 3 Arena source code: it's one of the better reads out there, as far as C is concerned. The Doom 3 source code is C++, but it's kind of weird C++ and I would be wary of learning C++ from it. Carmack has spoken about how his C style is just so much more mature than his C++ style, and this is exacerbated in these examples because Q3A is the last game in C, but Doom 3 is the first game in C++.
Yes, he's an icon in the C world.
This is what I mean for quite a while, id Tech 4 was released in 2004!
That doesn't make Carmack any less of a great developer in how he pushes the limits of current hardware.
I'm not sure if my thought is obvious or insightful, but I like it. I try to write all my new general/reusable code as pure functions whenever possible (which is almost always).
Too true.