Re: I'm a noob here.

[Shark8 <OneWingedShark@gmail.com>]

On 05-May-14 05:28, sdalemorrey@gmail.com wrote:
> Hello,
>
> I've recently been placed at the head of an effort to completely
> retool a forex engine. The original developers wrote the thing in
> PHP (frontend) and C (backend).
>
> There have been issues with code sanity mostly related to the size
> of the numbers being dealt with.  It is not uncommon for a single
> pass through the order match engine to generate numbers in excess
> of 10 Billion, and we're tracking up to 16 decimal places internally
> on some trades.  Obviously float would be a bad idea.  The initial
> Java prototype was using BigDecimal and that helped a lot, but there
> seems to be a bit of information loss when you do math on numbers
> which don't have the same scale.  Other issues were encountered as
> well so a new project was launched to uncover a language that could
> handle this sort of work more easily.

Given it was PHP I'm actually surprised you didn't list PHP's 'helpful' 
automatic methods for string/numeric conversion as one of your 
trouble-points.

> After a lot of research, I selected Ada as the platform upon which to
> build the next generation of this engine. My general feeling is that
> Ada has the best approach to minimize bugs long term, even if there
> is a learning curve upfront.

I don't think you'll be disappointed.
One technique you could use is separating out user-input (or other data 
which is possibly 'tainted' or non-conformant to your expected format) 
via private type and having functions to return the proper, safe, 
internally used type(s).

> What I'm having a hard time wrapping my head around though, is what
> is the difference between Ada and Spark?

SPARK is a subset of Ada -- the only one.
Its goal was to provide for (and facilitate) safety-critical 
applications by restricting what Ada features would likely generate 
nonsense, what constructs were impossible to check/prove, etc.

> What I don't understand just yet is HOW does it do that?

SPARK is also a tool: it integrates a prover utility into itself so that 
you can more easily use formal methods in software construction.

Ironsides is a DNS written in SPARK, and the authors have written a 
couple of scholarly papers on it for showing (a) the strengths 
formal-methods, and (b) that formal-methods are ready for mainstream 
industry-usage, and (c) that safe software needn't be slower than the 
unsafe.


Read these two papers and you should get an idea of /how/ SPARK works:
1 - http://ironsides.martincarlisle.com/globecom_2012.pdf
2 - http://ironsides.martincarlisle.com/ICRST2013.pdf

> I've tried to follow the Ada Gems articles and the best I've been
> able to glean is that Spark appears to not allow assignment during
> compare i.e. none of C's if(a = b) garbage.  Which is great, and
> all, but why a whole different profile just for that?
>
> Or is Spark a derived language, much as C++ is derived from C, and
> I'm just not really groking it properly?

You can't do that in Ada either.
SPARK is a proper subset, not a derived language.
The SPARK profile/subset is designed to reduce the Ada language to a set 
which is easy/feasible/possible to run a static prover on -- not the 
elimination of [strictly speaking] common mistakes in the language.

> I'm sure I'll have tons of other questions going forward, but I'm
> excited about learning a new language as I undertake this project.

Great, ask away -- c.l.a has some great people.

> My initial role will be Architect but then I'll also be the
> development lead.
>
> My own background is C/C++/Java and I have about 15 years experience
> in software development with the last 5 years of that in the
> Architect & Project Manager role.
>
> This is actually the first time in half a decade where I'll need to
> be "the guy" who functions as an SME on a new language, so I need
> learning resources to come up to speed as quickly as possible.

Ah, tutorials and learning resources aren't exactly prevalent -- 
compared to, say, Java or C or C++ but there are a few around.

I taught myself mainly from the John Barnes *Ada 2005* book, the *Ada 
2012* book should be available soon. See: 
http://www.amazon.com/Programming-Ada-2012-John-Barnes/dp/110742481X/ref=sr_1_1?ie=UTF8&qid=1399310596&sr=8-1&keywords=Ada+2012

> I'm glad this newsgroup exists and I hope you guys/gals don't mind
> me leaning on you for advice from time to time.
>
> Any caveats with the language might be good to know about as soon
> as possible.  I took Pascal classes in high school and Ada looks
> like it derives some of it's syntax from that. It's also possible
> that Pascal derives it's syntax from Ada, but either way they seem
> to be in the same family.

Ada was based on Pascal because its design as a learning language gave 
it many desirable features that addressed the 
strawman/woodman/ironman/steelman requirements.

You don't really have to "watch out" like you do for gotchas like you do 
in C/C++/PHP because the language is remarkably free of them -- you can 
depend on the compiler to catch a *lot* of what you're used to having to 
do 'manually' -- so feel free to "play around" with it some.

The only big 'gotcha' that comes immediately yo mind is misunderstanding 
tasks:
1 -- Inside an accept/do block there is no concurrency, this is inside 
the rendezvous and so the tasks [caller & callee] are bound together.
2 -- A task which isn't finished will keep its declaring-parent from 
exiting, so you may have to force/allow the close yourself w/ a "done" 
entry if, for some reason, you cannot use an OR TERMINATE on a select 
statement.