Do you think Hack is a good language to start a new project in, compared to non-PHP languages? Are you using Hack for things besides the main web page?
Yeah, I think Hack is a good language to start a new project in. For as much flak as PHP gets, there are actually a lot of good things about the language. The fast development cycle -- edit php script, refresh -- is something amazing that you don't get in a lot of statically typed languages, which usually have a compilation step. The crazy dynamic things you can do also occasionally have their place, though it's certainly easy to shoot yourself in the foot.
On the other hand, a lot of the time you want the safety that strong static typing can give you. Even just the null propagation checking can immediately find tons and tons of silly little bugs without even running the code, and ensure that the code stays consistent as a "mini unit test" if you will.
Hack hits the sweet spot of both. Wiring the Hack typechecker into vim was really revolutionary for me -- having both the immediate feedback of the type system for all the silly bugs that I was writing, along with the fast reload/test cycle from PHP, is great.
You seriously think that? That's how we do haskell web development. Both yesod and snap do this out of the box. That's how every java developer I know works.
Edit: I misread what you wrote. I thought you were saying there was something fundamentally different about the type checker, but more that reload experience is different then what you get with Yesod.
How big is your code base, and is it all in one huge file or something? Our stuff is reloaded and ready before I've alt+tabbed back and hit refresh.
Once you have type annotations, it wouldn't be too much of a stretch to enforce them statically with a separate tool. You could even go as far as rejecting first-party code if you can't statically determine every single value's type. Pylint's underlying astroid library has a bunch of inference tools you could perhaps build on top of.
FB already had a PyLint-like tool earlier that could do some static analysis, namely pfff (also open source and written in OCaml), but it did not provide a full-on static type system like Hack. (Background: I used pfff when I was in bootcamp at FB itself. This was however prior to hack, I worked solely on C++, Java, and a bit of Python at FB after bootcamp).
I am sure if FB started off with Python, a similar solution could have been found, but if you're looking for a tool that exists _right_ now, Hack is actually quite decent.
Creating a static type system, implement local type inference, as well as working out "gradual typing" and associated problems (all while being able to do type-checking at speeds developer _expect_) is not a trivial problem.
For that matter, can you call a typed function from an untyped one? Or, worse, a typed method? If the typing is purely static, there's no way to know the method you're calling is actually typed, so there's no actual guarantee that it receives the types it's declared unless your entire program is typed. It doesn't seem like a very strong guarantee if both the caller and the callee have to opt into the typing.
If you're looking for a tool that exists right now, you either have an existing codebase and can't port it to Hack if it's not already PHP anyway (for the same reason Facebook couldn't port away from PHP), or you're starting from nothing and could just use a statically-typed language in the first place.
I don't know if I'd even be excited about the prospect of optional static typing in Python. (It hasn't gotten me interested in Dart, for example.) I'd kinda rather see the effort poured into something that could do static duck-typed analysis/inference, e.g. balk if I pass an argument that could be a non-string into a function that tries to call `.startswith` on it. (Ah, but maybe it could theoretically be a string or None, and I only know it isn't None for reasons the type system can't see, and now I hate the type system.)
I didn't say it was a trivial problem. I just don't feel excited by the solution.
Another mode (you specify the mode per file/compilation unit) is "strict". In strict mode, you can not code any un-typed code (note, the standard library is typed with hack).
(There is a bit more nuance here, but you can read that in the documentation.)
So the idea is to eventually migrate most of the code to strict, but code that relies on legacy can remain partial and you can write new code without waiting for a re-write to finish.
See http://docs.hhvm.com/manual/en/hack.modes.strict.php http://docs.hhvm.com/manual/en/hack.modes.partial.php
"Shapes" are also a neat feature specifically for parts where static typing can be frustrating for dealing with HTTP requests specifically: http://docs.hhvm.com/manual/en/hack.shapes.php
(FWIW I don't see myself using Hack, but I'm not a web developer. I'd say the ML family languages are my favourite, but for what I do day-to-day it's not really an option.)
I'm intrigued, because it's such a good idea (especially when null's originator claimed it was a "billion dollar mistake"), though Java doesn't have it. I'm wondering if there's some subtle problem with it...?
Also, how do you make your vim typechecker fast enough? Usually, even syntax colouring is local to ensure adequate performance - and a typechecker with inference/propagation would be very non-local.
and an Optional<T> class (references to which can still be null for maximum hilarity): http://download.java.net/jdk8/docs/api/java/util/Optional.ht...
I'm stoked. And disappointed the "elvis" operator didn't make it in.
I hope some day Java breaks backwards compatibility and eliminates null entirely. Then again, that's already happened with the proliferation of other JVM languages. But that doesn't me at my day job, where we have a large legacy code base... which would need to be ported to a backwards-incompatible version of non-null Java anyway. Hm.
Well, with Java 8 I can at least start to grow null-safe code within our codebase.