Gradual type checking for Ruby
github.com
github.com
This is certainly useful sometimes, as it gives programs the desirable "fail fast" property. But it isn't "typechecking" as most engineers understand it. Or at least, it should be clarified that this is run-time typechecking. As such, it negatively impacts runtime performance, unlike compile-time typechecking.
This project also seems to miss the primary opportunity of run-time type checking: checking properties that are difficult to prove statically! For example, checking that a number is even, that a string is lowercase, that an index is within the bounds of an array, etc. These exotic types require a dependent type system to be checked statically, but in a dynamic environment they are trivial to verify.
Two suggestions for improvement: 1) add "sum" types (i.e., discriminated unions), and 2) let the user define their own types via lambdas, such as PrimeNumber.
It basically seems equivalent (albeit somewhat nicer in a few ways, ie. scalar types are supported) to PHP's "type hinting"[0]. I will say that it is useful, in combination with unit testing, as you can pick up on problems with things slightly easier than hoping for the best in production and tailing error logs, but proper static type analysis is more useful.
That being said, sum types would be a nice addition to this library.
You can get a statically-typed Ruby here: http://infraruby.com/live
It follows Java's type system (including generics with bounded wildcards) but it doesn't support Ruby reflection.
> When most practitioners think of "typechecking", they typically think about proving properties about programs statically.
This is what the type theory community (e.g. Bob Harper) thinks...not anyone else from what I can tell (definitely not practicing programmers).
Typing it out on mobile didn't make it easy to do the right quote context. Here is a good essay about it all:
http://www.cl.cam.ac.uk/~srk31/research/papers/kell14in-auth...
vs. say
https://existentialtype.wordpress.com/2011/03/19/dynamic-lan...
There are other ways to do typing that might make more sense for a dynamic language than going down the expressiveness rabbit hole; e.g.
I'm not saying that types or typechecking are inherently static concepts. I'm also not saying that this library should do static typechecking—that would be an absurd demand. I only meant that the wording is misleading.
Even more misleading is author's use of the term "gradual type checking", which has a well-understood meaning: the ability to add static checks to an otherwise dynamically-typed program.
Most programmers don't think "dynamic type checking" is a misnomer, while it is true that "type checking" itself leans towards a static connotation.
I've seen gradual type checking used both ways in the literature, actually. Wiki has the term defined for dual phase:
http://en.wikipedia.org/wiki/Gradual_typing
> Gradual typing is a type system in which variables may be typed either at compile-time (which is static typing) or at run-time (which is dynamic typing), allowing software developers to choose either type paradigm as appropriate, from within a single language.
I'm sure this is just poor writing (as Siek defines it, it should be from dynamic to static), but there is enough confusion here where you might bother using the term for adding stronger dynamic type checks to an otherwise less dynamically typed language (if you admit dynamic types as types, of course). Also, a dynamically checked type signature is the first step to a statically typed one (as long as your types remain weak enough that static typing is achievable in the future). So in that sense, it is "gradual" typing, just from a meta perspective :)
For example, in our application code, we'll use a warning for some type coercion for example
if isinstance(obj,Bar):
warnings.warn('Using a Bar as a Foo!')
But in our tests, we do want hard failure (so we can phase out the behavior as much as possible before removing the functionality). So we do something like the following:
if TEST:
warnings.filterwarning('error','Using a Bar as a Foo!',RuntimeWarning)
It's very useful, even if warnings is a bit too much about regex matching for my tastes
I'm fairly sure it changes the performance characteristics of code it is applied on. I'd recommend adding benchmarks to the README so prospective users might be aware of this beforehand.
Ruby is flexible enough to allow quite a bit of experimentation with stuff like that. Especially because classes can be re-opened, so if worried about performance, it'd be easy enough to allow type annotations (or whatever other extensions people come up with) to live in separate files if people want them to, and conditionally include them only as needed/wanted.
It's much easier to use defensive coding techniques at runtime without having yet another framework in there that anyone who wants to read the code has to learn. Typing a few lines less is not really a benefit when it basically increases code complexity.
A lot of languages (Java, C#, Go, etc.) have very inexpressive type systems, and that tends to make many dynamic language developers wary of them. Contracts has a very expressive type system though. It understands duck typing, adhoc union types, and a bunch of other stuff that makes it a great fit for a dynamic language.
Plus, we've disabled it in production, so we get coverage in test/development mode, but no performance penalty in prod. I look at it as an extended form of testing. Type contracts are very quick and easy to add, and they help tests catch additional errors. They're also useful in code reviews. Sometimes I'll have to search for 5 or 10 minutes to figure out what kind of thing is getting passed in, where the contract makes it perfectly clear.
The best part is that the contracts are optional. If some method takes wildly differing arguments and it's going to be a pain to give it a contract, then don't.
This is the best tool I've added to my Ruby arsenal in some time. I strongly recommend taking it for a spin.
What I meant was that contracts in a language like C# give me the ability to statically verify the program at compile time. It is not a "nicer way to add conditional testing logic" but a way to formally prove correctness in my programs.
In some cases, sanity checking can happen up front/at compile time. In other cases, these must occur at runtime.
The Pragmatic Programmer has a whole section on contracts; it is pretty good.
I like the aproach Perl 6 took on gradual typing. You can read about it in this article which computes fibonnaci's number:http://blogs.perl.org/users/ovid/2015/02/avoid-a-common-soft...
The only reason I wait for the next winter to come is because Perl6 will be production ready by then as Larry Wall announced at FOSDEM this year.
typesig def meth(arg) arg end, [Numeric] => Numeric
Although it's still end of the method, it already suggests that signature will be there
Disclosure: this may be a Bad Idea (TM)
* It would be better if this didn't pollute the global namespace by defining `#typesig` in `Module` [0] -- perhaps consider refactoring that method into a module which the user may extend. Doing so would also get you out of needing to define `Module#prepend` for older versions of Ruby.
* Perhaps allow the user to enable/disable type checking at a global/class level. For example, then users could only enable type checking during specs if they wanted.
* Instead of using class-level variables, try using class level instance variables. They have less odd behavior when dealing with subclasses [1].
[0] https://github.com/gogotanaka/Rubype/blob/develop/lib/rubype...
[1] http://www.sitepoint.com/class-variables-a-ruby-gotcha/
Edit: Whitespace
The OP is eduardordm, which can be found right underneath the article link. If you look on his HN profile, his GitHub name is also eduardordm.
The repo author is gogotanaka.
So, no. He's not. And the repo author is consequently unlikely to ever see your comments.
Not only are these simple checks to make, but it's extremely bad practice to scatter commentary about a project everywhere across the internet; people who only know about this project through GitHub would not see your comments either.
typesig :sum, [:to_i, Numeric] => Numeric
also, the global switch is simple:
if $DEBUG
require 'rubype'
else
def typesig(*args) end
end
Recently I've had to pickup Hack for work, and if there's one thing I really like about it is the type hinting. The best part is that it helps you handle nullable types (not sure if it's done here).
When I switch back to Ruby from Hack, I find it harder to reason about my program.
http://www.cs.umd.edu/projects/PL/druby/
Some features:
--------------
Type inference:
DRuby uses inference to model most of Ruby’s idioms as precisely as possible without any need for programmer intervention.
Type annotations:
Methods may be given explicit type annotations with an easy to use syntax inspired by RDoc.
Dynamic checking:
When necessary, methods can be type checked at runtime, using contracts to isolate and properly blame any errant code, similar to gradual typing.
Metaprogramming support:
DRuby includes a combined static and dynamic analysis to precisely model dynamic meta-programming constructs, such as eval and method_missing.
Then we interface with the AST of any language and we can stop re-iventing the wheel every two week...
It is so crazy ?
Nobody tried it before ?
Think about it, how would you handle type annotations in an agnostic type checker?
Now I do have a table of symbols and their type.
At this point its just a matter of using the AST to being sure that everything is correctly typed...
Am I wrong ?
Since I still like ruby's syntax, my hopes are that crystal (http://crystal-lang.org/) will one day become more mainstream (and maybe be adapted to some extent in mainstream ruby).
https://www.ruby-lang.org/en/news/2014/01/10/ruby-1-9-3-will...
https://www.ruby-lang.org/en/news/2015/02/23/support-for-rub...