Why Ada Is the Language You Want to Be Programming Your Systems With
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I've talked about this history with engineers from the 1960s-70s. They did not regard the introduction of Ada as a good thing. The JOVIAL language had been developed by engineers and modified through experience over several years to become something they were quite happy with. The impetus that led to Ada came from management and implementation was done by academics.
Unfortunately I was laid off before I got to write very much of it, but it seemed like a neat (if cumbersome and old fashioned) language.
Information about it is pretty hard to find, and there's no open source or free compilers that I know of, but here are some links I had saved.
A 1980s style tutorial:
https://apps.dtic.mil/dtic/tr/fulltext/u2/a142780.pdf
The mil-spec:
http://everyspec.com/MIL-STD/MIL-STD-1500-1599/download.php?...
An explanation of how it came to be:
The government has an extreme aversion to encouraging competing approaches or internal competition - largely because of budget concerns around double-work - which drives this behavior.
Just the mojo required to print an integer (having to instantiate a generic) was considered complicated
Ada was also very slow to compile, on the order of 10 times slower than Jovial. (my experiences)
Avionics systems back then were tiny. Jovial usually ran on a 16 bit processor.
Ada enabled a certain maturity and correctness to the avionics domain.
But as the recent Boeing debacle has shown, the avionics domain is in need of greater sophistication and reliability. What it doesn't need is more hackery, as satisfying as that may be for the hardware hackers.
Though Ada isn't a massive household name, I think its designers were vindicated by history.
[0]: http://www.inf.fu-berlin.de/inst/ag-se/teaching/V-EMPIR-2011...
Standardization means less autonomy, which generally means that the opinions of prestigious people are imposed on everyone else. This can be good for intellectual rigor at first if your social pecking order is based on having sound opinions, like St. Augustine, but if it's based on anything else, standardization is an intellectual disaster from the start. And of course standardization prevents intellectual progress, always and everywhere, which is how Galileo ended up under house arrest.
Regardless, this entire incident was precipitated by boeing, and the carriers, not wanting to have to retrain pilots on the new systems.
Note that the bug which caused the Ariane V disaster was written in Ada. And that was caused by the language. If the Ariane V code was written in C and the value simply overflowed, nothing negative would have happened. (The value would be hilariously wrong, but that wouldn't have mattered because the code wasn't necessary during flight. It was an oversight that it was running at all.) However, this is Ada, so it caused an integer overflow exception. Which was uncaught. Which caused the entire system to nope out. Which caused the rocket to blow up.
So there's that to consider.
So... what you're saying is that the language not recognising an exception conditional has occurred is a better outcome in mission critical applications? "wasn't necessary", "It was an oversight", "Which was uncaught"... With these phrases you've already pointed out that the developers had improperly implemented the application.
Yes ideally the programmers should have handled the exception, but once your in production and the system is running, should you really just halt the whole program due to an exception the prograera didn't foresee?
Assertions are also usually turned off for performance reasons, not to allow the program to plow through invariants being violated.
For a banking application, yes, die, hard, as loudly as possible. Downtime is worth it. Do not continue, do nothing until it is understood and fixed.
When you're flying. Hmmm. Not so much. Dying is a really bad idea. Ok you should have it tested thoroughly so it isn't going to happen but if it does and "anything could happen" well "anything" is better than killing all the passengers, crew and anyone you might crash on, right?
Literally anything is better than that.
Idealy, you log it, you refuse to take off again, all the fleet is grounded etc etc but deciding to fall out of the sky because something unexpected happened is probably not the right response.
Is graceful shutdown possible? No? Ok, so take your chances and log noisily is a less bad option.
I think that is the crux of this debate. In my background, yeah, you fail hard when anything unexpected happens. It's the most straightforward way to fail safe.
But my background maps better to the financial case; I've never worked on avionics or anything like that. I can see the point, though, that, in that kind of situation, failing hard doesn't fail safe at all.
It's conceivable to me that different problem domains require different default behavior. (And perhaps, by extension, different programming languages.)
> It's conceivable to me that different problem domains require different default behavior. (And perhaps, by extension, different programming languages)
Not sure about problem domains, e.g. 3D graphics is the main problem domain in videogames people play for fun, and CT scanners which save lives.
Different projects indeed have different requirements.
Every time you see a programming-related holy war on the internets (exceptions/status codes, static/dynamic typing, unit testing or not, FP/OOP, etc.), you can bet the participants have different types of projects on their background, and these projects needed different tradeoffs. More often than not, what’s good for a web startup aint’t good for Nasa or MS, and vice versa.
Brings to my mind: Erlang
I design for mission critical things on a regular basis, and one of the error modes I must accommodate is random bit flipping by cosmic rays, emf, or other failures.
Sometimes, it is possible to push things to a "safe" failure state and reboot (which often takes only 100 ms or so)
Sometimes, though, the error must be caught and corrected to a last known good value or something like that. Everything critical is sanity checked : overall boundaries, rate of change, state related boundaries, etc. Layers of "reflexes" are more robust than a single programmed behavior, because an error in one will be resisted by the others. So much the better when there are segregated systems to check each other.
Often, I'll have a "brilliant" system that performs to a very high standard and is complex and brittle. If the brilliant system fails, it just shuts down or reboots. Underneath the brilliant system is another layer or two. A "competent" system that is simpler and more robust, but less efficient and with soft failure modes, and a "brainstem" system that takes nothing for granted, even checking basic functions by bit flipping to negate stuck ram bits or broken ALU logic, but only tries to do a pasable job, reducing algorythmic complexity to its bare acceptable minimum.
Typically the system will generate a basic range of acceptable parameters at the lowest level (and take corrective action if needed), then refine the range at each subsequent level..rinse and repeat. That way, each lower level checks the ones above.
Or, you just fail downwards if errors are suspected. Either way.
Designing failure tolerant systems is not impossible, but it requires a different mindset.
There are plenty of situations when automated or manual recovery isn't possible and/or where carrying on with a potentially damaged system can make things worse. In practice, you solve this sort of problem via other design solutions, like redundancy. If you think that a critical system needs to keep running, but you also think that some errors will have to be handled by shutting it down, then you make it redundant.
Airplane FBW systems are a good example (caveat: I don't do airplanes, I do medical stuff -- I might be wrong about the practical details of this but I think it gets the point across). If the ELAC (elevator and aileron computer) runs into a condition it doesn't know how to handle, there's a good chance it will make things worse if you keep going. But you also don't want your mitigation to be "just halt the damn ELAC", you still want to have control over the elevator and the ailerons. That's why there are several ELACs.
More to the point: if something has to keep happening, no matter what, then you design the computing system and the firmware around it so that it keeps happening.
> At design time you better figure out what all the error cases are
Not being able to figure out what all the error cases are has been an unfortunate component of systems engineering for decades now. The Wright brothers would have probably been able to account for all the failure modes in their flight control systems, but today, you are likely to miss some of the failure modes of a CPU that executes nothing but a NOP and a jump back to that NOP.
With the exception of simple and special-purpose systems, built without any programmable logic whatsoever, it's unlikely that you'll be able to figure out what all the error cases are. (There's something to be said here about OISC and whatnot...)
That's not to say it's OK to build systems that blindly steamroll over errors -- just that you have to build them so that they can deal with errors that you have not foreseen at design. You will run into that sort of error sooner or later, we are all failible.
Edit: as for assertions, performance may be a factor, but that's not why you want to turn them off in production builds for embedded systems. (Although, IMHO, this isn't the right approach for embedded systems at all, but I've seen it used).
First of all, you turn them off because, presumably, they make your system deviate from the spec (i.e. the system ends up handling some cases differently in the production build vs. the debug build, and hopefully the one in the production build is the one you want).
Second, you turn them off because they can introduce undefined behaviour in your system. For example, if a peripheral gives you an incomplete or malformed packet in response to a command, or fails to answer altogether, you may want to abort with a stack trace in a development build. But what you really want to do IRL is probably to check and reset that peripheral, because for all you know it may be stuck and giving haphazard commands to an actuator.
IMHO, assertions are only a partial answer to the problem you really want to solve -- obtaining useful data (e.g. stack traces) in response to error conditions. You can generally log the useful data in addition to actually handling the error correctly. Development and production builds should differ as little as possible -- ideally not at all. Handling potentially critical errors in different ways certainly doesn't count as differing as little as possible.
Surely, the pilot should always be able to have the last say in where or what the plane is flying toward? Or are these planes now so complicated the pilots can't fly them without the computers?
Airplanes that cannot be flown without computers definitely do exist. The F-117 is perhaps the most famous. Its shape makes it aerodynamically unstable on all three axes and it needs constant correction from the FBW system. Which has quadruple redundancy :). You can turn off the autopilot in these systems, obviously, so you get to say where it goes -- but without the FBW system to issue corrections, the plane crashes.
As for Boeing (or Airbus, who have this ELAC thing)... the main thing to understand here is that there is not a computer. There are several computers, each of them covering a particular set of modules (e.g. ELAC controls the ailerons and elevator, SEC controls spoilers and elevator). There's a more in-depth overview here: https://aviation.stackexchange.com/questions/47711/what-are-... . The autopilot is only one of them. The way they take over each other's functions is actually remarkably advanced, and leads to very interesting procedures for handling failures, see e.g. https://hursts.org.uk/airbus-nonnormal/html/ch05.html .
Now, on some airplanes, some actuators can only be controlled through these computers. They get the commands from the pilot and they issue the right signals that control the actuators. There's no way to bypass them. You can turn off the autopilot and the plane goes where you want but the actuators that control the flight control surfaces are still acted upon by computers.
I don't know if this is the case on Airbus specifically (like I said, I'm in a different field), but if it were, then simply turning those systems off in case of something unexpected is definitely not the right design solution.
I agree that the concept of the top-level handler and customization should be more visibly documented.
Why? It's totally possible to infer the most general type for all the functions in the program, hence to infer the type of the needed handler.
Any language with subtyping and powerful type inference can do this, here is the toy ocaml example with typed algebraic effects (you can think of them as of exceptions):
val read_file : path -[ Not_found ]-> string
val process_content : string -[ OOM | Intern_err of int ]-> float
let computation path =
let content = read_file path in
let result = process_content content in
if result < 0
then raise Bad_result
else result
val computation : path -[ Not_found | OOM | Intern_err of int | Bad_result ]-> float
Even if you want to keep some exceptions unhandled, you can easily choose which ones, and track them carefully.
But it is indeed possible to have a single top-level handler (or a carefully constructed hierarchy of handlers) that explicitly handle all exceptions that may arise. (And to ignore an exception is also a form of handling.) The handler already exists, but it's pretty simple: for any exception it prints the error and terminates the program. It's up to developer to override this to make the program more robust.
The acceleration problem was caused by noise flipping bits in the RAM the operating systems used to store state data. (The Toyota code was most immune to this because they duplicated their state by storing it in two different places, always compared on read and if it was different rebooted. But the OS was provided the the chip manufacturer, NEC which was a black box to Toyota - and it wasn't as conservative.) On rare occasions a bit flip would take out the watch dog process and the cruise control just after it decided to accelerate, and occasionally if that happened everyone in the vehicle died.
Toyota blamed the deaths all sorts of things for a while - the driver, the carpet, third party accelerator pedals. Which to my mind was fair enough. They like everybody else had no idea what was causing it, but they knew their monitor / reboot if out of spec kludge worked very well so it was unlikely to be the ECU.
Simply switching to a language with a stricter runtime may automagically take care of some simple cases, but no system is devoid of failure modes.
Overflows are classic sources of disastrous bugs (e.g. the infamous THERAC-25). Switching to a system that detects them and raises an exception is a step in the right direction, but you still have to handle the exception cases correctly. And in some cases (like the Ariane V), incorrectly handling an exceptional condition turns out to be worse than allowing it to happen.
But let's say this was something unexpected - then probably the only way to mitigate this would be a backup system - but this is an unmanned system - and Apollo/Saturn/Shuttle/Soyuz levels of redundancies is not required.
How could anyone believe this system was safe? No testing or requirements needed.
To test your invariants, you should sabotage the spec and check that invariants break.
Once your spec passes model checking (or perhaps theorem proving with TLAPS), you can codify it in e.g. ADA-SPARK contracts.
Once you have that, you've validated your spec, your contracts and your code. Bugs can only occur in your invariants and the seams of your subsystem. This level of rigor should be standard by now for safety-critical systems.
That is true, but I found that in more strict languages you have a bit of a slower ramp-up, but the time you save later before production in bugs you don't have could be used to take more looks at the spec and better simulations.
>If the Ariane V code was written in C and the value simply overflowed, nothing negative would have happened.
In this particular case yes, however if the system was actually needed for flight (which I would guess most software is), it might be better to reset and retry.
On average if your language fails hard like ADA it's also more likely to find these bugs in simulations and tests.
Rust might have solved the problem the way you like it. Integer overflow causes exceptions only in Debug mode, not in Release mode.
In many of these large companies in avionics (and not just avionics), the people writing the specs are not the same as the people writing the code. There is no trade-off between how much time it takes to write the code and how much time it takes to draft and review the specs.
Edit:
> On average if your language fails hard like ADA it's also more likely to find these bugs in simulations and tests.
That is definitely ture, but it's important to keep two things in mind:
1. The possibility of a hard failure from your runtime is something that you need to be aware of at design time. As seen in the case that the parent comment mentioned, there are cases when a hard failure on a non-critical error is actually worse than allowing the error to occur.
2. More important, if it's hard failures that expose bugs during tests, the first thing you have to fix, even before you fix the code, is the test cases themselves. A hard failure during testing is an indication that the test cases you have don't cover a given situation and, more importantly, that your system can't even handle that situation.
There are always going to be error conditions you can't recover from, and if they're in critical systems, you work around that (e.g. through redundancy). But a runtime that gives you a hard failure is rarely useful by itself.
Except overflow would most likely have caused a significantly more severe outcome than the uncaught exception.
And there is a restriction in GNAT (No_Exception_Propagation) which forces you to deal with any exception immediately, and should be used in any critical software imho.
https://docs.adacore.com/gnathie_ug-docs/html/gnathie_ug/gna...
This is not a language issue, but a general engineering one. In any critical system that can cause an unexpected exception and failure, there should be sufficient redundancy, so that when the main system goes down, the failover system can take control.
That sounds complicated to me, in 2019 with 25 years of C++ experience. (And of course C++ error message sprouting mysterious stdlib templates also seems complicated to me).
PutLine("The number is " & num);
printf("The number is %zu\n", num);That it's as easy as printf demonstrates the changes in thinking to today fairly well.
and then
int_io.putline(num);
with Ada.Text_IO; use Ada.Text_IO;
with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
...
PutLine(num);
[0] https://www.adahome.com/LRM/83/RM/rm83html/lrm-14-03.html#14... (Ada 83 Manual)
Languages with these modules and import statements should be burned. (Starting with Python.)
For pete's sake, couldn't they at least combine this with and use into one keyword so you don't have to repeat yourself?
Or can't use be made to forgive a missing with and just get on with the show?
Do defense contracts pay by the byte or what?
Nothing different than std in C++.
Though a single use declaration will get you the identifier in C++, the right header file has to be #included. At least it's possible for a single include to bring in lots of material:
#include <biglib> // just one of these
use bigfoo::bar; // one per identifier
use bigwidget::zark;
class foo {
foo();
~foo();
};
foo::foo()
{
}
foo::~foo()
{
}
(The C++ people are self-conscious about verbosity, and trying to fix the problem; unfortunately, in wrongheaded ways that are making the language worse.)
So far as I can tell, you dislike how verbose the Ada "hello world" is, because it supports namespaces, and uses them. That wouldn't be something I'd agree with, especially not when dealing with any program of significant size.
It's the only benchmark that we have any kind of analysis for (https://www.researchgate.net/publication/3188171_The_Confoun...), which correlates to less defects and less time per feature. Less code is better. Until I see evidence to the contrary, I think it's a valid criticism. YMMV
Holy crap; are they really saying that all the various correlations seen between numerous software metrics and fault proneness are actually the effect of nothing but raw size?
That's so intuitive. Because in our daily experience, almost all reasonable approaches to to various aspects of program organization actually work fine in programs of a size that one programmer can comfortably fully understand and maintain. Even for any technique reviled as "bad" and discouraged in coding standards, there are counterexamples of it working fine. Those counterexamples are in the context of small programs, so we are told, "just wait, that approach will burn you in a big program". But it looks like what will burn you is just the size of that big program, no matter what techniques you wield, whether blessed or not.
That little paper you pointed to there (thank you) looks pretty darn important.
class foo {
foo() = default;
~foo() = default;
};
The idiomatic way to write your class is just:
class foo { };
The purpose of the C++11 default mechanism is to request a default implementation of a special function in situations when it would be suppressed. For instance
class foo {
public:
foo(int x); // this will suppress the default constructor
foo() = default; // this requests it back
};std::cout << X;
is not a generic, but on the project I just tested, if I substitute X with a type that does not implement an appropriate operator<<, I get ~1000 suggestions in the overload set, many of which are generic operator<< that are templated on a `typename OStream`.
I personally find having to do overload resolution first on a 1000 function overload set containing generic and not generic functions, and then often having to actually instantiate a generic (doing template argument deduction, template instantiation, substitution-failure is not an error so the next overload might be picked, etc. etc. etc.) infinitely more complicated than "just" instantiating a generic.
That certainly sounds like academic self-righteousness.
Impression of mine back then was academics were busy designing their perfect languages to do data transformation while ignoring real world engineering needs and that not everyone had an unlimited account on the schools big iron mainframe.
I remember using Ada 95 in university, after learning C++, Java and Python in other projects. It worked very well for concurrent processes, but it was so basic as a developer experience.
In C++ (98 I think) I needed to build length dynamic arrays, in Ada 95 I had to build dynamic length strings.
Ada95 did have dynamic strings, they were provided by Ada.Strings.Unbounded package.
>crafted the Steelman language requirements, a series of documents stating the requirements they felt a programming language should satisfy. Many existing languages were formally reviewed, but the team concluded in 1977 that no existing language met the specifications. Requests for proposals for a new programming language were issued and four contractors were hired to develop their proposals [1].
The success of the language resulting from this process was ensured by the D of D's strong desire for a standard programming language shared by all of its contractors.
[1] https://en.wikipedia.org/wiki/Ada_(programming_language)#His...
”Dijkstra was known to be a fan of ALGOL 60, and worked on the team that implemented the first compiler for that language. He was closely involved in the ALGOL 60 development, realisation and popularisation.”
Also: Haskell and pascal over C++ and Java (https://www.cs.utexas.edu/users/EWD/transcriptions/OtherDocs...)
I've never come across any indication that Dijkstra wrote actual code (in the sense of something executing on a computer) after 1970 or so. The algorithms in the EWD notes are all written in ALGOL style pseudocode.
Dijkstra was the CS equivalent of the Patent Law concept of a "Non-Practicing Entity", which gave him great liberty to troll all programming languages without exposing his own choices or designs to corresponding scrutiny.
It's more accurate to say that CS is no more about computers than aerodynamics is about flying: Without flight, aerodynamics would barely exist as a distinct field, and wouldn't be of interest to anyone except people in a sub-field of fluid dynamics, and never intersecting with practical concerns such as materials science and the overall design of buildable objects. Similarly with CS: Without computers it would be a simple, obscure sub-field of mathematics, about where it was in the 1930s when Post and Turing and Gödel were active, and it wouldn't intersect with fields like electronics or, probably, have much to do with formal grammars.
In the version of Ada we had, it was DOS based, but I found out that you could use the interrupt API, allowing VGA graphics.
There is something to be said for a language that was written to a spec from the beginning, however. That is a luxury that few languages today can claim; most language specs were written after the first version(s) of the language were implemented, and were written to match the implementation, not the other way around.
Writing the specification first makes for a much cleaner language, though not always the most comfortable, if you put any weight in your own opinions.
[I am speaking generally from here onwards and I am not looking for specific examples to the contrary. I know full well that there are exceptions to the generalizations below.]
Lots and lots of engineers today would (and do) express complete comfort in their daily drivers of C and C++, while producing buffer overflow bugs and use-after-free bugs all the while. Maybe it isn't in the best interest of the software landscape to let developers choose the languages they use...
We have, as a community, let our feeling that software development is an art dictate how we react and deal with new information; we overwhelmingly reject it. What we're doing now is so much more comfortable, and we feel like we know what we're doing with [language x] finally! Why would I want to overturn all that comfort?
Software development is not an art, it is a science, and we've been ignoring the science part of that as we refuse to abandon our favorite language(s) for things that could easily be proven to be better, if we would just do the testing to determine performance numbers, ease of bug introduction, ease of maintenance, and so on.
We call ourselves "software engineers" and we don't measure anything beyond the most rudimentary measurements. We DEFINITELY do not actively look to overturn our comfort in favor of finding a better language to use. We don't try to improve anything the moment that might mean that we switch languages, no matter how significant the long term advantages could be. We don't even think about what the long term advantages could be; we're too busy telling ourselves that we are smart and that we can do it in whatever language we are comfortable with.
Other important metrics no one thinks to measure:
* Quality of compiled assembly or bytecode (it is dead easy to write a shitty compiler that produces stupid assembly or bytecode)
* Runtime performance on tight loops (this is directly tied to cost when running on something like AWS Lambda, and code that performs well means you need to upgrade your hardware less often)
* Lines of code required to achieve a given goal. Less is obviously better, when you understand that more code = more complexity, and that more complexity = higher likelihood of bugs. Also, if there is enough boilerplate code to break these guidelines, then what is that code doing, except slowing development times and slowing execution times?
I can write a method two or more ways and know provably which is faster. No one does this! No one looks for hot spots and tries to optimize them. No one profiles anything if performance is deemed "good" or "not a problem."
There is a lot of CPU time to be saved, a lot of RAM usage and cache optimization that no one does because they believe that their work is above being challenged, even by themselves. This world is insane.
Just look at the web front end. Absolute cluster fuck.
An arithmetic bug in a flight safety system or financial trading platform? Your odds of being successfully sued just went up astronomically as it's much easier to show negligence and put a dollar figure to damages.
Professional licensing regimes are principally designed to prevent negligence by a priori preventing people from holding themselves out as capable of performing some task. In terms of legal liability all they really do is restrict the extent to which you can limit your liability contractually. That's important in business and in professional services (doctor, lawyer, etc), but for downstream users who suffer damages there was never a contract involved, anyhow.
https://www.ordemengenheiros.pt/pt/a-ordem/colegios-e-especi...
Although you can get by without the admission exam, some kind of state projects do require it for any engineer putting their name on the contract assignment.
I haven't touched it in a long time, but I remember some of the impressions it made on me when I first used it.
The type system: I think you could do some really fancy things like:
speed := miles_traveled / elapsed;
the thing is, I think you had to create some conversion stuff for the "/" so that it allowed two types to be divided, returned a third type.
unchecked conversion: no matter what you did, you had to interface with hardware. So there was a lot of unchecked_conversion() stuff to convert between basic machine stuff.
argument lists: You couldn't have a printf() or any other varargs type stuff that I remember. This made interfacing with external libraries that needed this kind of stuff lots harder. (maybe there are ways to do this)
there were things I really did like
the package and package body stuff: You could implement a bunch of interfaces, and compile against the prototypes before the implementations were written.
the attributes, like foo'Size and the system package let you write your code to be correct even if system types or machine types changed
A lot of Ada is really tedious, but once you got over that, working with an existing project was usually really nice.
Well, that was 5 days ago, which means you CAN post the link! (I'd like to see it, quite a lot.)
Both seem to have good ecosystems, but quite different. Ada has more high-assurance tooling and practices. Rust has more in terms of packaging and general-purpose high level libraries.
With Ada, it's pretty hard to shake the feeling that it's not as welcoming. Either you are building a spacecraft, or "what are you doing here?". Not that anyone actually says that, and in my limited experience playing with the language, everyone seemed nice. It's just a feeling that's hard to escape. I wish it weren't so, because I think Ada has a lot going for it and it could be good in more donains.
One kind of cool thing is that it's designed to get by without so many heap allocations, and it does some interesting things to allow/encourage more stack allocations. It also has more sophisticated runtime checks, like contracts, that are kind of between a unit test and a compile-time check.
Rust is great at managing complexity. I keep holding out hope that Ada can somehow give us some simplicity back while still making useful software.
There's significantly more attention provided to things like Wasm than there is to things like embedded use cases for example.
The two languages, ecosystems, and communities seem to have largely non-overlapping objectives despite having overlapping technical capabilities.
Things might be better, but last time I checked rust's compiler was a lot slower than C and the binaries were several times bigger. That last one is a big deal for embedded.
Embedded people care.
> Nobody wants to play with their compiler to get a small binary... If rust can produce small binaries, then it must produce small binaries.
Everything is a tradeoff. Smaller binaries may or may not perform better than larger ones. This is something you need to play with, just like in C. If one single setting made everything the best in all circumstances, it wouldn't be a setting. C compilers have these settings too.
> Languages are typically judged by their defaults.
As I mentioned, the defaults have also been adjusted to help out too.
Code size isn't the only axes that can be used to measure the quality of a binary, there are many others: like run-time performance, portability, debuggability, etc.
No C compiler I know optimizes for size by default, in fact, I don't know of any C compiler that, by default, optimizes anything at all. Clang, GCC, MSVC, and all other mainstream compilers require users to enable optimizations (O1, O2, O3, Ofast, etc.) and none of these are code-size optimizations. Only relatively recently have compilers grown the ability to optimize for size, and you have to go way out of your way to do it (enable Oz, disable debug information -g0, enable LTO -flto, ...).
Optimizing for size over anything else by default is one of the worst trade-offs a compiler can make. It's a bad trade-offs for most programs, and it is a bad-tradeoff for most compiler users.
In terms of real impact on developers I never felt it was dramatic. The rust language support in editors is so good that you will catch most errors before compiling. So once everything is dealt with you usually compile and it just works.
Binary size is also one of these areas they are dealing with atm.
I keep thinking servers should be written a bit more like embedded thingies. (Though I suspect the actual trend is in the other direction).
Both kinds of software deeply interested an asynchrony and concurrency (though not necessarily parallelism). And both also tend to talk over networks to other gadgets as part of a complex system. And since my job often revolves around putting out fires when severs OOM, I'd also like to see a lot less malloc().
It would be nice if software could place hard upper limits on how many resources (including RAM) it takes to serve a request and then reject requests early. With real-world languages and frameworks, we can only do very primitive approximations to this. But a framework written from the bottom-up with a malloc-is-evil mentality () might be able to do it.
Layered on top of that we can also ensure that if at runtime your device memory configuration is sufficiently different from what your assumptions were at compile-time, then we don't allow the device to boot so that you don't end up in a dangerous resource exhaustion situation by accident.
We use this for no_std embedded shaped use cases, but you could also use this library and programming model to create a special heap in your normal programs which have statically tracked allocations to create some region of your program context that you want to have assurances like that.
We have 3-4 things kind of in that vein in our pipeline to open source, and I think that's number 3.
Rust is a language developed by its users. The reason less things happen in Rust embedded domain, is because less companies pay people to work on embedded Rust than they do on WASM rust.
EDIT: on a second read, it's not clear whether the article is saying we should use Ada the next time we are building a rocket, or the next time we are building an OS.
Do people think part of missile software includes “npm install wordpad”?
The biggest challenge is to prove that it works. The space software community historically is very conservative and risk-averse, and mostly for good reason. As Kubos (and hopefully others) get more flight heritage with Rust on the flight segment, it'll be a much easier sell.
That's the biggest obstacle I think. Someone will have to break the seal and establish that "Rust in Space" actually succeeds consistently, then larger "trad space" organizations will follow.
"Code is read more often than it is written". Reading Ada is so unambigous, and clear. If you mean if then, you have the keyword then, when you want to say procedure you say procedure and you can read that. Rust? fn, because is it fun, or functor, so fuck you.
Yes, I do want to read out what I type and possible speak it to collegues without sounding like I have a fn seizure.
The problem is that "fn" is optimizing the WRONG things: not only is your code going to be read more than it is ever written, but this abbreviated form is actively hostile towards domain-level subject-matter experts that you may want to audit or verify your code. Now, instead of him jumping into code that reads like English (Ada), now he has to 'decode' Rust BEFORE AND DURING his evaluation of the code, distracting him from his purpose.
Cd is rd m thn it is wrtn, it is esr to rd function thn to prse fn rclnt function and cont rdn.
A somewhat amusing endorsement given that the infamous failure of the maiden launch of the Ariane 5 due to series of interconnected software bugs - a reminder perhaps that the choice of implementation language does not automatically make for a reliable system.
(4 failures in the 14 first launches, but only one partial failure in 91 launches since).
Ada can do overflow checking, so choice of language can have an impact on reliability, but the software engineers deliberately disabled some of those checks to save CPU cycles on a computer that was running at/near capacity. Their reasoning was that it was impossible for the variables in question to overflow given the known flight characteristics... of an Ariane 4.
This is not correct. It was, in fact, "some software bug caused by Ada", in the sense that in most other programming languages, the error that did in fact happen would have been harmless.
For those who are interested, the full report is at http://www-users.math.umn.edu/~arnold//disasters/ariane5rep..... There is no need to "guess" when a fairly detailed public analysis is available, particularly when the issue is one that comes up repeatedly. It is true that the problem was that a horizontal velocity variable ("horizontal bias", BH in the code) overflowed, although it was not the ordinary kind of integer overflow, but rather a floating-point-to-integer-conversion overflow, which does not produce an exception in any commonly-used programming language.
The missing piece of the explanation is that the variable in question was no longer being used at that point in the flight, so if the failure had been allowed to pass silently rather than shutting down the SRI ("inertial reference system"), the rocket would not have been destroyed.
Of course, under some circumstances, allowing variables to have grossly incorrect values in your inertial reference system could have been equally disastrous — that's what you assumed happened. The system was designed in the way it was because the assumption was that such errors would almost surely stem from hardware failures rather than software bugs; perhaps that is a "domain issue caused by a failure in management and testing".
But in some sense, you can argue that any organizational failure is a "failure in management", since management's job is to look to windward and steer the organization clear of failures by any means necessary. But in fact the particular failure in management that happened was for the software to be inadequately thought out, such that one of Ada's hidden pitfalls caused Ariane 5's maiden flight to fail.
Also as long as we're buttering up the mods, don't forget sctb!
Something all that fancy type system should have prevented. I found it interesting in the Hackaday piece that the C code xample called out the size of an integer while the Ada version did not. The Ada version caught an implicit conversion, but apparently does nothing for overflow.
Every language has it's good points and bad. I still want to learn more Rust. In fact I recall reading recently that some Ada developers want to adopt something akin to Rust's borrow checker. All I know is that C++ is not safe. How well does Ada work with C libraries? Rust is pretty OK at it.
https://learn.adacore.com/courses/intro-to-ada/chapters/inte... shows how Ada's Interfaces.C package and the Import and Export aspects are used to share data and make function calls between Ada and C.
I understand that people are conditioned to think APIs are easier to consume when they're in the standard library, because that's true in many languages, especially those that lack a modern package management system (e.g. Ada). But it's not true in Rust and there are advantages to having libraries like `libc` outside the standard library. For example `libc` is updated more frequently than the Rust standard library (multiple times per month vs every six weeks).
Yes, there is. Not only is dependency transitive: you now depend on everything libc depends on — but now you're depending on the correctness AND properties of the dependency, to include security.
This is not entirely correct. The code which overflowed was unnecessary for flight. People have this idea that the sensor sensed it was going 32745 m/s to the east one moment, and -32723 m/s the next, and then tried to compensate for the sudden gust of wind it must have encountered. This is incorrect. The routine in question was only supposed to run when it was on the ground, and served no purpose in flight. It was scheduled to be disabled 40 seconds after launch. (The flight failed after 37 seconds)
The problem is specifically the fact that the code was written in Ada. Ada does not fail the way other languages fail when you overflow. Instead of given an incorrect value (which never would have impacted the flight) it throws an exception. This exception was uncaught. This uncaught exception brought down the entire flight control system, despite the fact that the falling code was not controlling flight.
Rust improves upon this situation by panicking in debug mode and wrapping in release mode, which is better than the Ada behavior in every possible way. Normal "unsafe" languages improve this by giving an incorrect value as the result, which in the case of Ariane V would have saved the flight.
Also Ada does have wrapping arithmetic available. It just isn't the default.
> "Rust improves upon this situation by panicking in debug mode and wrapping in release mode, which is better than the Ada behavior in every possible"
So... What you're trying to tell us is that Ada recognising an exceptional situation has occurred is bad, and that Rust just ignoring it is a good thing? Righto... An integer overflow occurring in this scenario is an exceptional condition. In this case it was one that the developers did not anticipate. This issue arose because they mistakenly thought it was not possible for this scenario to occur. The mistake here was not anticipating the exception and handling it in a meaningful way, not the raising of an exception. The fact that not raising an exception would have avoided the disaster in this case is entirely incidental. It was still an exceptional circumstance that the developers, testers, designers did not anticipate. The silent wrapping behaviour you describe would have bitten someone eventually, perhaps here, perhaps somewhere else. Possibly with enormous repercussions.
> "Normal "unsafe" languages improve this by giving an incorrect value as the result, which in the case of Ariane V would have saved the flight."
The normal "unsafe" languages you're referring to ( presumably C ) have a history of very poor error handling. Requiring an extremely high degree of conscientiousness when programming for mission-critical applications. Can you imagine actually programming for what you're describing here? Not only does the computer have to guard against outright failure, but now it has to infer the possibility of an error state from a stream of in-band data in real-time. Righto...
Also, just so you know: Signed integer overflow is UNDEFINED BEHAVIOUR in C.
Probably the fact that the engineers got the case analysis wrong suggests that the methods of reasoning they were using weren't very effective. Modern formal methods might or might not have helped; guaranteeing that a piece of code is statically free of exceptions is not a terribly advanced thing to do, but really you'd like to guarantee that the variable was actually big enough. Having less code to reason about certainly would have helped.
C’s choice is clearly unconscionable.
I don't think there's an open-and-shut case that error values are "preferred or beneficial" in general with respect to exception handling through nonlocal control-flow transfers; there are reasonable arguments on both sides, and it seems likely that both are viable options in most circumstances, and which is better depends on those circumstances. (For example, lazy evaluation or catastrophic consequences attached to software crashes would seem to me to weigh heavily on the side of using error values, while interactive REPL-style usage would seem to me to weigh on the side of nonlocal control flow, perhaps with Common-Lisp-style restarts.)
My point was narrower: in this particular case, using error values analogous to NaNs, rather than shutting down the SRI, would have saved the rocket, without posing the risk of using garbage data that C's semantics pose. In this particular case, they would have been better. It's possible that, in other cases, perhaps even in other places in the SRI firmware, using error values would have been worse than unwinding the stack or shutting down the SRI. But in this case they would have been better.
(If you aren't convinced of that narrow point, you should probably read the report from the Lions board of inquiry.)
In the general case, the Ada behavior of detecting and signaling numeric errors seems to be the only robust choice to me. The alternative could only be acceptable if it's proven that the algorithms fail safe in the presence of tainted data.
However, default-ignore vs. default-explode isn't a difference between handling errors with IEEE-754-qNaN-style dataflow-tainting and CLU-style nonlocal control flow transfers, as you seem to think. In either case, algorithms that need data that could not be computed successfully will fail to get that data; in either case, you can write the code to either propagate that failure or to attempt to recover from it somehow. In either case, you will not be able to control the spacecraft if you needed that data to control it. The difference I was mentioning, which is not generally applicable, is that in unusual cases like the Ariane 5 disaster, where the erroneous data shouldn't have been computed in the first place because it wasn't needed, qNaN-style error handling clearly results in safer behavior.
But, in general, real-time control is not a place where there exists a "robust choice" when your software is broken. If your jet engine control software or your antilock braking software is broken, you're likely to die, and no error handling strategy can prevent that, at least not at the level we're talking about. Biological systems manage this situation by having a melange of somewhat-independent control loops using different algorithms that are constantly fighting for control of the organism; while this does seem to produce systems that are more resilient than engineered systems, it's less efficient and enormously more difficult to develop or understand, and it's the opposite direction from the rigorous certainty you and I favor.
Rust tries to give you zero-cost abstractions where possible. Overflow checks aren't zero-cost, therefore they're disabled in release mode. Otherwise when safety can be done at zero-cost (at runtime) Rust will usually do that.
I agree with you though that the exception might have helped in many other situations, especially if a simulation catches it early on. I would still say from gut feeling that ADA makes the safer decision on average.
And of course the run-time checks can also be disabled for Ada of course, and usually are for release build.
> These runtime checks[1] are costly, both in terms of program size and execution time. It may be appropriate to remove them if we can statically ensure they aren't needed at runtime, in other words if we can prove that the condition tested for can never occur.
> This is where the analysis done by GNATprove comes in. It can be used to demonstrate statically that none of these errors can ever occur at runtime. Specifically, GNATprove logically interprets the meaning of every instruction in the program. Using this interpretation, GNATprove generates a logical formula called a verification condition for each check that would otherwise be required by the Ada (and hence SPARK) language.
[1] overflow check, index check, range check, divide by zero
---
So again, I do not see why Rust would shine (as some people suggested) here, Ada/SPARK can statically ensure that your program is correct and eliminate all sorts of runtime errors, including overflow.
When I learned Ada (blog post somewhere in this thread) I was pretty shocked by how many more runtime checks it had than Rust does, overall. Rust usually checks things at compile time.
That's perhaps an oversimplification; elsewhere it's been said of Ada's mentality that "Incorrect Is Simply Not Allowed." — but there's ALWAYS been a preference for pushing checks from dynamic to static, and from runtime to compile-time.
As a trivial example, the following code is typically generated without any sort of index check because the loop-control variable takes its range from the Array, it's obvious that it CANNOT be an invalid index, and this is allowed by the language reference manual (and encouraged by the annotated reference manual)—
For Index in Input'Range loop
Input(Index):= 0; -- Zero the array.
End loop;
Value : Positive := Positive'Value( Get_Line );* The biggest thing I miss is that every block was inherently a try-block. Just put your exception handlers at the bottom of the block. This provided a nice separation of "normal flow-control" and "exceptional flow-control". Why have try-catch anyway -- I never got used to that later in life.
* Exceptions were not synonymous with errors. In fact the way to read a file byte by byte was just to keep reading bytes and never explicitly check for end-of-file. Let the exception handler handle this case. Logic is much cleaner.
* Remember that you can't just dump core and shell out to the OS on an un-handled exception -- not if your controlling a ICBM flying of the continent. Ada really forced you to handle all errors at some level of the call-stack with an exception handler. At the outer-most level -- just call self-destruct.
That's still the case in Ruby, you can put a rescue at the end of the block.
I observe the same effect on other things like unit tests except the effect is the reverse of what people typically think. Lots of unit tests early on help you write correct code initially but as code matures it's just wasted automation time & it can end up ossifying some architectural decisions (ie. a change ripples out & causes a large amount of tests to need updating).
When I worked in EDA I was given a project to get rid of linting errors in our generated HDL code. We generated both VHDL and Verilog. Our generated VHDL had very few problems thanks to strong typing. But there were lots of problems to fix in the Verilog code caused by it's weak typing.
I wonder how nice a PL/SQL & Ada combined environment/IDE could be.
Also random note, but wouldn't most engineers familiar with HDL's be electronic engineers rather than software developers?
Basically, the US is a really bad place to be an electrical engineer specializing in electronic hardware, but it's a great place to be a software engineer or developer.
Its because software engineers get paid much better in addition to more options. As a firmware engineer I straddled both sides. So many of my EE colleagues lamented they should have done more on the software side. A few of the brilliant ones moved to places like Google, Amazon which need them for specialist roles.
I remember a decade back I was visiting a customer in Taiwan to help debug our product and saw a legion of Chinese engineers helping out some project. I knew eventually Taiwan would lose some of their R&D to China.
Also, there are lots of professional software developers who studied Electrical Engineering or Computer Engineering in college. Many schools historically had all their CS classes and faculty within their EE department.
Here are some examples. All classes are fundamentally floats. Errors are caught at compilation.
cInches i1, i2, i3;
cCm cm1, cm2;
i1 = 1.f; // error
i1 = cInches(1.f); // OK
i3 = i1 + i2; // OK
cm1 = i1; // error
i1 = i2 * 2.f; // OK
float f1 = i1 / i2; // OK
i1 = i2 * i3; // error! square inches are not inches
int add(cInches in1, cInches in2);
add(i1, i2); // OK
add(cm1, cm2); // error
I used to use a lot of doubles. The I wrote some DirectX and GPUs all use float. I figured if floats are good enough for 3D, they're good enough for me :o)
Single-precision floating-point starts you off with about 6-7 decimal digits of precision, and the intermediate rounding will mean that you're constantly introducing error in the 7th digit. Computer graphics are pretty tolerant of error--you only need about a 1-2 digits of precision generally--and achieving higher FLOPS is more useful than higher precision. Engineering tolerances are usually going to be tighter, perhaps 4-5 digits for particularly tight tolerances. Furthermore, you're more likely to use nastier equations (logarithms and exponents are particularly bad for precision), so single-precision could well introduce error with real-world consequences.
Although I'd like to add a typical issue when there's a small change in a large quantity.
Say time. If you measure time in microseconds, and use floats, your precision will be halved to 2 us in just 33.5 seconds. In 24 hours, the precision has detoriated to over 2 milliseconds. One famous example is the deadly Patriot missile bug: https://sdqweb.ipd.kit.edu/publications/pdfs/saglam2016a.pdf
> Furthermore, you're more likely to use nastier equations (logarithms and exponents are particularly bad for precision), so single-precision could well introduce error with real-world consequences.
Some other ones are iteration and simply long computation chains introducing systematic error.
Floats costing the same as doubles is a myth stemming from x87 arithmetic, which is obsolete. On an x64 CPU running 64-bit code, your compiler can often pack four floats into one SSE register. Even when that doesn't happen, CPU microcode can likely do more with floats than with doubles.
Lastly, memory bandwidth usage and cache occupancy doubles, which is true even with x87.
> Even when that doesn't happen, CPU microcode can likely do more with floats than with doubles.
I have no idea what that means. As far as I know, there's no CPU microcode dealing with floating point numbers.
> Lastly, memory bandwidth usage and cache occupancy doubles, which is true even with x87.
So use floats when you have a lot of data.
> The difference is meaningless in scalar code. Not everything is or can be vectorized.
Multiple scalars can be packed into one SSE register even in scalar code. This is not the same as vectorization.
> Pretty much no difference between one double and one float in a SSE XMM register.
Even then, some arithmetic operations have higher throughput with floats than with doubles.
> I have no idea what that means. As far as I know, there's no CPU microcode dealing with floating point numbers.
Your CPU doesn't execute the ISA directly in hardware, it first converts it into architecture specific micro-ops. That includes FP operations.
> So use floats when you have a lot of data.
That's not the point. A lot of the time, the cost difference will indeed be irrelevant. The point is that there is a cost difference.
They can, but can you honestly call it a common case for scalar code?
> Even then, some arithmetic operations have higher throughput with floats than with doubles.
By far the most (90-99%) of FP computation is additions and multiplications (or fused multiply adds). For scalar case (1 double or float in SSE register), they take precisely as long on modern x86 hardware.
Sure, float div executes in 11 instead of 13-14 clocks for doubles and I'm sure transcendentals are even worse, but they're rarely needed. Even then, if the dependency chain allows, the cost is often OoO scheduled away in integer dominated code.
> Your CPU doesn't execute the ISA directly in hardware, it first converts it into architecture specific micro-ops. That includes FP operations.
Except that SSE instructions pretty much are micro-ops as-is. Despite similarly sounding term, microcode has nothing to do with micro-ops.
> That's not the point. A lot of the time, the cost difference will indeed be irrelevant. The point is that there is a cost difference.
Well, I've written a lot of SSE, AVX etc. SIMD code. There sure is a big difference when you're processing large amounts of data. But... I've seen floats introducing silly precision related bugs [0] and a ton of useless float -> double -> float conversion chains. Most of the time most programmers should default to double.
[0]: Example: https://randomascii.wordpress.com/2012/02/13/dont-store-that...
From what I read about Ada, its types offer better guarantees than what's typically available in mainstream programming languages: https://learn.adacore.com/courses/intro-to-ada/chapters/stro...
Please default to doubles and optimize only when it's actually an issue. 99% of cases it's not, unless you're doing throughput computing. In that case floats provide up to 2x improvement. Keep in mind modern x86 CPUs can perform up to 16 double precision FLOPs (FMA) per cycle per core — do you really think it's going to be the bottleneck in your code?
32-bit floats expose you to nasty issues with even "simple" stuff like errors in naively computed sums. Issues that mostly just wouldn't matter if 64-bit doubles were used. See a proper floating point summation algorithm [1].
That said, even 64-bit doubles (or any arbitrarily long imprecise format) won't shield you from all of floating point weirdness. But it sure does help in common cases.
With floats you'll get issues like this:
https://randomascii.wordpress.com/2012/02/13/dont-store-that...
[0]: https://www.agner.org/optimize/instruction_tables.pdf
[1]: https://en.wikipedia.org/wiki/Kahan_summation_algorithm
That said, it seems to be arguing for something in a vacuum. Where is the mention of other new programming languages that also fit this category? Where is the mention of Rust? Rust fits all the same requirements:
- A general, flexible design that adapts to satisfy the needs of embedded computer applications.
- Reliability. The language should aid the design and development of reliable programs.
- Ease of maintainability. Code should be readable and programming decisions explicit.
- Easy to produce efficient code with. Inefficient constructs should be easily identifiable.
- No unnecessary complexity. Semantic structure should be consistent and minimize the number of concepts.
- Easy to implement the language specification. All features should be easy to understand.
- Machine independence. The language shall not be bound to any hardware or OS details.
- Complete definition. All parts of the language shall be fully and unambiguously defined.
The exception is possibly the last one, complete definition. But that's debatable as Rust does have a reference, but no one wants to go as far as calling it a spec. (Also, I know some people think Rust has some "unnecessary" complexity, personally I do not). The article goes on to compare to C, but doesn't mention some of the new features of C++ that make it safer, or Rust which is approximately as safe as Ada. So why would I pick Ada over other modern languages?
btw, I really enjoyed Steve Klabnik's post on learning Ada: https://words.steveklabnik.com/learning-ada
I'm not sure this is at all applicable to rust. Perhaps once there are more than the one, quickly mutating, implementation, we can say that it's easy to implement the specification.
> - Reliability. The language should aid the design and development of reliable programs.
This one feels a touch questionable, given the built-in "succeed or die" macros that simplify code at the cost of reliability. There's also the unsafe keyword, and how the impact of an unsafe operation in one section of code (say, an imported library) can have negative impacts on unrelated sections of code otherwise deemed safe.
> - No unnecessary complexity. Semantic structure should be consistent and minimize the number of concepts.
Borrow checker aside, there is a ton of complexity in Rust (traits, multiple flavors of arrays, multiple flavors of boxed values).
> - Machine independence. The language shall not be bound to any hardware or OS details.
Rust relies on the LLVM project to provide this, and relies on the contributors to the LLVM project to target different architectures.
Most of those are linted for, so you can use them to speed development but still be aware that they shouldn't be there in production code.
Whether it should or shouldn't be in production, following Ada's rules it wouldn't be allowed in the code in the first place.
That said, they are configurable, so I see your point - they are more permissive than what Ada allows
OTOH, I believe you can turn lint warnings into hard errors for only production, allow for fast development but programmatically disallowing them from reaching production. But again, thats configurable.
Yeah. Just like every line in C/C++ code can have negative impacts on unrelated sections.
While true, that talking point feels somewhat unfair or even in bad faith. Rust requires "unsafe" escape hatch to be able be a low level systems language. Or gasp, to call libraries using C ABI.
I write a lot of low level code in C/C++ (firmware, kernel drivers, low level services) and I think a C ABI compatible "runtimeless" safe language, like Rust, dramatically improve security, safety and even ultimately provide faster time-to-market.
No such thing.
You're well above 100% right with your points, if we weren't looking at the language criteria put forth by Ada.
EDIT: It's worth nothing that Ada is also a system and embedded programming language.
I would consider a program that dies early to be more reliable (but less robust) than one that just soldiers on, probably doing wrong (and possibly dangerous) things.
Regardless, it is the programmers choice whether to call panic!() or to try to handle an error gracefully and continue.
Really, there's a certain amount of software, like the Ariane 5 SRI, for which the only acceptable outcome is not to have the error in the first place — there's no acceptable way to handle it once it happens. That software is very expensive to write, so you want to keep it to a minimum in the overall system, but sometimes you cannot avoid having some of it.
The article is about Ada. If you want to read about Rust, go read about Rust.
I don't read the comment you're replying to as asking for an article about Rust or any other language. It's interesting to read about Ada, specifically. I would love to see descriptions of what Ada does better than other modern languages for systems programming. "Strong typing" is a feature of many non-C languages, for instance, but types with specific ranges aren't. And the "storage pool" mechanism deserves a more detailed comparison to other memory management approaches.
Yes, most systems programming is done in C and C++. Some people even use Rust, I've heard. Doesn't mean that an article has to draw comparisons to these languages. In fact, almost every article comparing programming languages inevitably does a poor job at it because the author most likely is more familiar with one language and then we'd have people criticizing the author because they got X, Y and Z wrong.
I have seen this a lot of time on HN. It's simply smart to not compare languages.
But yes, perhaps I was too critical, it's mainly the title that is a little misleading, and then the content didn't express anything specific about Ada that other languages don't also have.
1) The article is on Hackaday, a website for hardware hacking enthusiasts. Most programming articles on the site are geared toward low-level and embedded systems programming.
2) The end of the introduction section of the article ends with the line: "Ada might also be the right choice for your next embedded project."
3) The last section of the article "WHERE TO GO FROM HERE" points the reader to a related article about how to get started with Ada on a PicoRV32 RISC-V core, a small processor typically used in FPGA and ASIC designs, not the usual fare for desktop, server-side, or web programming.
Ada was designed for safety-critical, military-grade embedded systems programming. It excels in that domain and while it CAN be used for operating system and application programming, it requires a bit more effort than other programming languages because of the difference in idiomatic approaches and the built-in APIs.
The best reason I've seen is because it's already passed the hurdles in some industries as being a compliant language for their needs. That might be a good enough reason for some, but it's not one that's important to me.
But seriously now: the author didn't mention Rust because they probably don't even know it exists. I work in embedded and like to ask people offering courses / tooling / services around safety if they support Rust and the only answer I got so far is "no". A lot of those people either don't know about Rust or they don't care, because everyone's using C and C++.
Ada does seem interesting, but all the buzz seems to be about Rust. Perhaps Ada deserves more interest?
https://www.electronicdesign.com/industrial/rust-and-spark-s...
SPARK statically checked function pre- and postconditions and constrained types certainly look very interesting especially for embedded systems. And for a lot of other low level code as well.
Which is a shame, because Rust is a great fit for these use cases. Though there are a lot of ecosystem shaped things that present practical challenges too: things that should/could be in no_std but unnecessarily depend on std instead, a variety of cargo workflow issues, etc.
There's a group in Germany (I think) that proposed attempting to qualify Rust to get it approved for inclusion in the list of 61508 languages, but that proposal did not seem to be met with much enthusiasm.
We're using Rust to build tools to service those kinds of industries, and it's non-trivial to justify its use even in adjacent tooling. Let alone to be directly deployed to a target device.
https://ferrous-systems.com/blog/sealed-rust-the-pitch/
There's still a lot of interest; this stuff doesn't happen quickly.
I would be thrilled to death for that effort to move forward with zeal however. If a WG develops around it, I'd also happily provide engineering resources to coordinate and work on the effort.
You should get in touch with the Ferrous folks, I'm sure they'd love to hear from you.
It's not necessarily as much Rust as the desperate need to get something safer than C/C++ without compromising performance and interoperability.
Object Pascal
D
ATS
Common Lisp
Ada
even Fortran!!
the list can go on and on
If it's just a matter of marketing and failing the subjectivity of a popularity contest, that's a shame, but I wouldn't leap to assume that's the sole reason.
On the other hand, think that some of those languages have commercial compilers being sold for decades and they are still in business.
So, some companies do value the quality of the software they product.
Additionally, modern Ada (after the introduction of SPARK, what 15 years ago now?) offers even more safety features that I've not seen in Rust, through the form of code contracts. Conttracts which can be used as run-time checks, and (to some degree) as static proofs about the code.
Extend Rust's type system and add a contract mechanism, then it'll have the same use-case that I have for Ada.
> SPARK builds on the strengths of Ada to provide even more guarantees statically rather than dynamically. As summarized in the following table, Ada provides strict syntax and strong typing at compile time plus dynamic checking of run-time errors and program contracts. SPARK allows such checking to be performed statically. In addition, it enforces the use of a safer language subset and detects data flow errors statically.
Contract programming:
- Ada: dynamic
- SPARK: dynamic / static
Run-time errors:
- Ada: dynamic
- SPARK: dynamic / static
Data flow errors:
- Ada: -
- SPARK: static
Strong typing:
- Ada: static
- SPARK: static
Safer language subset:
- Ada: -
- SPARK: static
Strict clear syntax:
- Ada: static
- SPARK: static
---
Additionally, safe pointers in SPARK: https://blog.adacore.com/using-pointers-in-spark and https://arxiv.org/abs/1710.07047.
---
Cryptographic library in SPARK 2014: https://github.com/Componolit/libsparkcrypto.
> libsparkcrypto is a formally verified implementation of several widely used cryptographic algorithms using the SPARK 2014 programming language and toolset. For the complete library proofs of the absence of run-time errors like type range violations, division by zero and numerical overflows are available. Some of its subprograms include proofs of partial correctness.
---
Ada/SPARK is excellent for real-time and safety-critical software: https://www.rcs.ei.tum.de/fileadmin/tueircs/www/becker/spark... to give you some ideas. It may be a bit outdated in some regards, though, for example: "Next version of SPARK 2014 under development (pointers!).". It is already done! :)
Ada was designed for programming safety-critical, military-grade embedded systems.
Rust was designed as a memory-safe, concurrency-safe programming language, largely to overcome the shortcomings of C++.
Each excels at what it was designed for, but the intended use cases are very different.
Rust is not (currently) being used for aircraft flight control systems--Ada is.
Ada is not (currently) being used for high-performance web browsers and servers--Rust is.
While there are SOME similar design goals in terms of memory safety, concurrency safety, and error prevention, they do not "overlap almost entirely in use case".
C/C++ have been great for embedded work, but Ada and Rust are better alternatives in my opinion. They are safer, more powerful, and more secure.
> F* (pronounced F star) is a general-purpose functional programming language with effects aimed at program verification. It puts together the automation of an SMT-backed deductive verification tool with the expressive power of a proof assistant based on dependent types. After verification, F* programs can be extracted to efficient OCaml, F#, C, WASM, or ASM code. This enables verifying the functional correctness and security of realistic applications. The main ongoing use case of F* is building a verified, drop-in replacement for the whole HTTPS stack in Project Everest. This includes verified implementations of TLS 1.2 and 1.3 and of the underlying cryptographic primitives.
> Its type system includes dependent types, monadic effects, refinement types, and a weakest precondition calculus. Together, these features allow expressing precise and compact specifications for programs. The F* type-checker aims to prove that programs meet their specifications using a combination of SMT solving and interactive proofs.
Still Go.
Ada:: n. A {{Pascal}}-descended language that has been made
mandatory for Department of Defense software projects by the
Pentagon. Hackers are nearly unanimous in observing that,
technically, it is precisely what one might expect given that kind
of endorsement by fiat; designed by committee, crockish, difficult
to use, and overall a disastrous, multi-billion-dollar boondoggle
(one common description is "The PL/1 of the 1980s"; hackers find
the exception handling and inter-process communication features
particularly hilarious). Ada Lovelace (the daughter of Lord Byron
who became the world's first programmer while cooperating with
Babbage on the design of his mechanical computing engines in the
mid-1800s) would almost certainly blanch at the use her name has
been latterly put to; the kindest thing that has been said about it
it is that there is probably a good small language screaming to get
out from inside its vast, {elephantine} bulk.
[0] http://catb.org/~esr/jargon/html/B/bondage-and-discipline-la...
[1] http://catb.org/~esr/jargon/html/L/languages-of-choice.html
Later on I experienced the famous feature of Haskell in which it takes a while to write a valid program that compiles at all, but then the program immediately works correctly the first time and is free of several large classes of bugs.
So yeah, excellent description of that trend!
Edit: another closely related phenomenon is people gaining a new appreciation for formal grammars and formal specifications, understanding how hard parsing problems are and how bad the consequences of underspecification and undefined behavior can be. I imagine in the Jargon File heyday it would have been made fun of to use formal specifications everywhere, but now some of the most successful systems and tools use them to good effect. Maybe there was a "formal methods winter" or "formalism winter" to parallel the AI Winter?
Edit 2: also, as a sibling comment mentions, these tools are much nicer to use now than they were then. Protobuf and friends do something akin to what ASN.1 did, but the tools around them are so much nicer!
During essentially this entire time period, the scale of what people were programming was growing much faster than the scale of what people could prove correct. If the aspirational task in 1995 was to prove correct a telecom switching system, the aspirational task in 2005 was to prove correct an AJAX frontend in untyped JS with its goofy coercion rules speaking over an unreliable network with MITM proxies to a backend written in untyped PHP, storing its data in a MySQL cluster where it would read from a read slave that was different from (and a poorly characterized latency period behind) the master it was writing to. Since then things have gotten more complicated, but I feel that formal methods have closed a bit of the gap.
However, I don't think of Ada as being a promising part of these developments. It isn't especially formally tractable, and it doesn't even attempt to offer the kinds of safety guarantees that Rust does. Rust, CompCert, seL4, Z3, Haskell, OCaml, and TLA+ seem a lot more promising than Ada. Heck, even Hypothesis is kind of in that category for me.
P.S. I miss you. I hope you're doing well.
(Many of the early criticisms of Ada seem a bit silly in hindsight. For example people used to like to make a big thing of it taking three or four years for fully standards-compliant compilers to appear, which seems pretty good going compared to, say, C++98. Similarly, hardware from the early 80s sometimes struggled to compile Ada code efficiently, but it turns out that processors were getting faster rather rapidly around that time.)
Another thing was a take on the Jargon File entry where a good amount of hacker backlash was due to it being a language forced by the DoD, so of course it is going to be bad.
Ada's "elphantine bulk" is smaller than many modern languages, and even some which the Jargon File praises, like Common Lisp. Its inter-process communication and exception handling functionality were relatively forward-thinking at the time and would look familiar to your average Java programmer.
Now, at the time, I didn't mind Ada (I think I was the only one to not mind it in class), but learning it just after K&R C/ANSI C (C was just recently standardized), it did appear to have quite a bit more overhead than I was used to.
It's a tongue-in-cheek document, made by imbeciles, not some real language evaluation...
[1] http://pixelscommander.com/wp-content/uploads/2014/12/P10.pd...
Does anyone know of a guide for writing C code where you allocate a specific block of memory at the start and then use that for all data from then on? Avoiding malloc is one of the suggestions there and seems like a smart strategy.
You're right, but you should still constrain yourself to these few instances to use malloc instead of wildly using it everywhere.
Basically we treated the heap like a stack of large context oriented memory blocks. Each of these blocks contains fixed data loaded from disk (static game resources like bitmaps, UI layouts, etc) and fixed size pools of fixed size game objects. The big blocks would get allocated in a stacked manner at distinct times like game title load and level load.
So if your game has bullets, you have a memory pool of say, 100 bullets to maintain the state of each instance. If you try to shoot a 101st bullet, you either don't or you have an ejection strategy. You never malloc or free during gameplay : you only allocate from one of the pools.
When it's time to unload the level... boom, you free the whole block at once, popping this stack. This is extremely efficient compared to freeing many individual malloc allocations.
Also warnings as errors, alongside static analyzers.
I quite like the way it eschews too much abstraction and can go from very low level to high level with a lot less code (and less bugs).
Given the current interest with IoT and the proliferation of cheap micro controllers it might be due for a resurgence(?).
Current micros are a bit big for Forth, though. You can run C or C++ on them. If you have only 4K or 8K of code space and 128–512 bytes of RAM the case for C over Forth gets a lot weaker. Maybe we'll see a resurgence of Forth when we get nanobots.
There's a flaw in the article:
Ada doesn't define standard types like int or float...
It does, technically, Integer and Float. The rest of the article is fine.
Lastly, it's amusing to see the Rust advocates cry out due to this. As I like to write, Ada is used in critical systems such as ballistic missiles and trains, whereas Rust is used in Firefox.
You mean to say that Ada is good for much simpler, easier, smaller-scope projects?
(I am neither a Rust nor an Ada user.)
I am obviously teasing the OP, but there's IMO a lot of truth to it. Safety-critical stuff damn better be simpler, smaller and fundamentally easier or it will fail and kill people. That's why stuff like https://groups.google.com/forum/message/raw?msg=comp.lang.ad... makes sense. In a lot of aspects, mission critical-software is much, much "easier": easier to stretch the budgets, easier to not have competition, easier to justify why something can't be done or why it has to take another 3 years of work.
While a modern fully functional web browser is a huge pile of complexity, technologies, requirements and yet it is still needs to work under much tighter social, economical and performance pressures. Any bug being widely exploited, could lead to people literally dying or at least having their lives ruined. It's just not as spectacular as "missiles".
So I think the OP (and probably you as well :P) is being arrogant by dismissing "firefox", that's all.
One system is taking a complex world and trying to reduce it to a safe and simple system - the other is taking something safe (some rando user inputs and a pile of HTML) and turning it into something complex - a rendered website.
Granted, I think value domain identification is one of the only ways for complex software to at all survive growing into a legacy system - so maybe the core difference is the nice stress free life of a system where the worst outcome of a critical failure is someone not being able to post on facebook ;P
1. Lets ignore firefox and JS and just assume we're in the 90's downloading HTML sites...
I remember fooling with Ada years ago and I really liked the concurrency and ipc mechanisms which was quite unique in the 00's. It was a little more friendly to use vs. pthreads. Now every new language is baking in concurrency. Since I wrote mostly c code I wound up making a franken program which was a statically linked Ada/c. I used Ada for its concurrency which called my linked in c code. It was a PLC emulator I scrapped.
Not to mention the bevy of advanced niche features, like SIMD support, and custom GCC extensions that lend superpowers to C coders that other languages typically lack.
Sure, ada may have it's benefits for certain narrow use cases, but for non-hobby projects spanning tens/hundreds of engineers, considering real world vendor support for ada and missing talent pool, C is the obvious choice
They sell a pro version with bells and whistles but AFAIK the actual compiler is the same.
I do prefer GNAT's error messages over AdaCore's compilers (despite the compiler frontend still being based on GNAT), but SPARK adds a ton.
[0] I should note that SPARK 2014 is also available as a GPL'd "community" edition.
EDIT: Asterisk + HN formatting
From SpaceX's 2013 Reddit AMA: https://www.reddit.com/r/IAmA/comments/1853ap/we_are_spacex_...
Its an interesting field, but feels hard to get into.
One wonders how much that's contributed to the lengthy delays in software delivery...
Regardless, it seems possible to eventually produce effective software using C++. ;-)
In this industry, knowing Ada could still be useful, even if only to read it.
Basically many industries that fall under the High Integrity Computing umbrella.
He wrote 3 books on Ada. http://www.cs.uni.edu/~mccormic/