Runtime verification in Erlang by using contracts | Hacker News Reader

Runtime verification in Erlang by using contracts

arxiv.org

138 pointslainon23 comments

Some day, after every language has taken its bits, we might actually see Eiffel in the real world.

Meanwhile, any of this available for Elixir, too? One of the languages on my 2019 list…

It's really easy to use Erlang libraries in Elixir. It's nice to be able to tap into an ecosystem with Erlang's maturity while still using modern tooling like Elixir.

Eiffel is used on the real world.

Just by companies that actually buy their software tools.

How do you think they are still in business, selling multiple variants of their tools?

I was going for a more publicly visible presence with "we might see". Don't know anything about the numbers, but I'd put Eiffel Studio with e.g. GemStone SmallTalk or Allegro Common Lisp or even current Delphi. Or, heck, Tcl/Tk and Ada, doesn't have to be about proprietary vs open source (cf. IntelliJ vs Eclipse).

But from what I've seen, I wouldn't mind it to become a bit more popular, more libraries, more publicly available applications. More rising tide lifting boats than secret weapon.

(NB: not that you'd need to be a secret weapon to keep a business afloat, there are a lot of companies that run on legacy support. There's nothing inherently better in paid software. Also: Eiffel the language vs Eiffel Studio.)

Eiffel the language has been available in some variants for free, for a couple of decades.

https://www.liberty-eiffel.org/

http://smarteiffel.loria.fr/

Just like with Smalltalk and Common Lisp, a language without the respective developer experience, isn't that attractive.

For a while SmartEiffel did enjoy some popularity, bindings to libraries where created etc. But it fell back, Eiffel moved on, and so did fickle OSS developers. And while Bertrand Meyer succeeded Niklaus Wirth as a professor at ETH Zurich, Eiffel didn't succeed Pascal in popularity as an academic programming language.

And did you actually like the EiffelStudio dev experience? I thought that was the weakest part of the whole offering (as opposed to CL and SmallTalk, by the way). And I like BON about as much as UML.

Yes, in the sense that it is much better than using plain vi or emacs. Smalltalk and CL are hard to beat, I do agree there.

I do enjoy using UML, not the extreme case of compiling UML to native code as promised in the 90's, but surely for application architecture and data flows.

I was quite pleased that my previous customer allowed externals access to their Enterprise Architect pool licenses.

it seems like this would be easier to implement in Elixir in a very idiomatic fashion. There's a lot of compile-time effects that Elixir uses, one thing that I'm playing around with (in an OpenAPI library I'm working on) is having the OpenAPI `response` contract be enforced on exit in :test and :dev compilation modes but removed in :prod mode.

I wish Eiffel Software changed their dual licensing business model so that more people would consider using the language in production.

Bertrand Meyer is constantly at the top of my “people to read when I’ve read all of my unread books” list and unfortunately the last time I looked those books were out of print.

My feel at the time was that Meyer introduced Eiffel right on the cusp of the move to free compilers, and he never recovered from that tectonic shift.

Whether most developers of that generation could be convinced that rigor was useful I cannot say (but fear the answer is “no”), but they certainly weren’t going to pay to learn or use a new language.

We certainly paid for our compilers and interpreters, even to learn a new programming language.

Alternative was making our own ones, from code listings.

That rigour is useful, having learned Eiffel, coming from Wirth languages background, reading Code Complete, completely influenced my way of writing C and I regularly used all the nice VSC++ ASSERT macros variants for pointer and argument validation.

Also adopted code contracts in Java and .NET years later.

Coming back to Eiffel, languages need a killer use case for business to adopt them, so they end up only having customers on domains where companies are required to take quality seriously, like high integrity computing.

And I wish it was still viable to make a business selling software tools to the average developer, instead of being forced to target only the enterprise, as the customers willing to pay for their tooling.

I worked on a large C++ project with design-by-contract pattern a long time ago. It was not the most pleasant experience. There was so much more code to validate pre and post conditions and class invariants. It might have had a lot to do because it was a classic OO business system (think a large Java app now, but where all the code was C++), but I remember spending more time writing the contract code than the actual business code.

Is there any recent writings on this pattern on applying the idea more sanely? As it is, I think I prefer to write testing code outside of the core behavior and have to anticipate what values are valid, or create new tests as bugs are found.

I think in languages like Eiffel that have first-class support for DBC, there’s less noise because the language is designed to propagate contracts appropriately (e.g. making subclasses inherit contracts from their base classes.)

Also, there’s been a lot of work in the Racket community on contracts: I think it has something to do with making Racket/Typed Racket interop safe .

It definitely seems like any OOPL would be inherently at a severe disadvantage in this style. In most Erlang code all you’d have to check are the function parameters.

One concern I have with their Erlang solution is that the preconditions and postconditions are expressed for the function as a whole, not each function clause. In some contexts, rather like OOP, a function can be quite different depending on the context it’s called with.

There's a whole "paradigm" called "light weight verification". I could point to particular papers, but unfortunately I don't know of a good survey article or exemplar tool/implementation/framework. But the term is very google-able, and skimming papers/tool descriptions will quickly give you a general sense for what sort of things are possible.

Contracts were developed into the C++ standard to make this easier: https://en.cppreference.com/w/cpp/language/attributes/contra...

https://github.com/tamarit/edbc for those who want to see the implementation

When trying to write a demonstration of how something works, why not make it expressive, explicit, and dead simple when attempting to demonstrate the utility of something?

It just looks like a thunk of code, with little rhyme or reason.

I gotta agree. The readme itself describes nothing. The code to me feels useless without documentation on how to use it.

Otherwise, I have to painstakingly go through their source or read 19 pages of small font. I don't want to do that.

"Accidentally" erased footage of the moon landing?!?

Wrong thread: https://news.ycombinator.com/item?id=19095849

Every time is correct but machine work vreification is no more like human finger work

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