[racket-dev] math collection [was: Hyperbolic functions]

From: Neil Toronto (neil.toronto at gmail.com)
Date: Wed Jun 27 00:05:30 EDT 2012

I haven't got a clue what you two are arguing about anymore. If you both 
stop, maybe Sam can implement that perfectly safe change to the typed -> 
untyped contract barrier that he said he could do. That would be nice.


Neil ⊥

On 06/26/2012 09:23 PM, Robby Findler wrote:
> On Tue, Jun 26, 2012 at 10:08 PM, Sam Tobin-Hochstadt<samth at ccs.neu.edu>  wrote:
>> On Tue, Jun 26, 2012 at 10:44 PM, Robby Findler
>> <robby at eecs.northwestern.edu>  wrote:
>>> On Tue, Jun 26, 2012 at 9:25 PM, Sam Tobin-Hochstadt<samth at ccs.neu.edu>  wrote:
>>>> On Tue, Jun 26, 2012 at 9:29 PM, Robby Findler
>>>> <robby at eecs.northwestern.edu>  wrote:
>>>>> This sounds like a terrible solution.
>>>>> There are lots of places in our system where we just declare facts and
>>>>> don't prove them and then use them for lots of things (often
>>>>> optimizations). Why should this one be special?
>>>> I don't know of any places like this in Racket.  What are you thinking of?
>>> The inliner and the JIT compiler and that whole interaction are the
>>> ones I thought of. I should have said "lots of facts" not "lots of
>>> places", tho. Sorry about that.
>> I'm still not sure what you're thinking of.  What operation does the
>> inliner or JIT perform that is justified by a
>> programmer-declared-but-not-checked fact?
> There are many operations that are implemented partially in JIT and
> wholly in the runtime system. The JIT generated version gets used
> unless certain conditions hold, in which case the runtime system
> version gets used. The programmer declared fact is embedded into the
> code and not specified as a fact per se, but for example, there is one
> such fact saying "this pile of assembly instructions is equivalent to
> the C implementation of list-ref, under the condition that the number
> argument is a fixnum less than 10,000 and we don't run out of pairs
> too soon" (roughly). There are large pile of such things. Another one
> you're probably more familiar with: "this pile of assembly
> instructions is equivalent to + when the arguments are both fixnums or
> both flonums".
> There is another pile of such invariants in the (pre-bytecode level)
> inliner. It relies on beta substitution and the ability to run certain
> primitives at compile time. (I don't know as much about that one, so
> probably there are more things it relies on than that.)
>>>> Certainly, Typed Racket is intended to be sound in the same sense that
>>>> Racket is safe, and that Haskell, OCaml, and Java are safe as well: if
>>>> you don't use specifically-marked unsafe features (such as the FFI and
>>>> `racket/unsafe/ops`), then you get a guarantee that depends only on
>>>> the correctness of the runtime system/compiler, not on the correctness
>>>> of any user code.
>>> Of course I understand this. I'm pointing out that this is not a
>>> significant guarantee, in and of itself (see last para below for an
>>> elaboration here).
>>>>   I think this a very important guarantee: we've seen
>>>> far too often that trusting user code in languages like C and C++ was
>>>> a big mistake in many contexts.
>>> I don't think this is an either/or. Indeed, just to continue with C:
>>> if everyone understood that the types were really just size markers
>>> and nothing else, then lots of the seeming unsoundness goes away in C
>>> (not all, of course, and as I've been learning from Regehr's blog,
>>> there are lots of other dark corners). But no one is suggesting we
>>> remove checks from array bounds, which is what really cost society
>>> money wrt to C and, IMO, the kind of invariant that matters.
>> I don't think the distinction that you're trying to draw here is
>> meaningful.  In particular, to return to our earlier example, if you
>> assert the type Neil gave for an untyped value, backed up with the
>> contract `(->  real? real?)`, then Typed Racket's type system can be
>> off by arbitrarily much -- no claim it makes can be trusted.
> I think you're making this out to be a boogey man, when it really isn't.
> But why doesn't your argument apply to any program that uses the FFI?
> It also invalidates all of the guarantees that TR makes. (And there
> are essentially no programs that don't use the FFI anymore.)
> And anyways, I think that TR actually makes *no* guarantees in a
> precise technical sense. Even if I accept the proofs about the models
> in your papers then (as I said earlier) we are not running your
> models. Why should you be the only allowed to introduce these
> particular bugs? I'm allowed to introduce other bugs, for example.
>> Further,
>> the optimizer will happily transform your program from one that
>> behaves one way to a different program, and cause the entire Racket
>> runtime to segfault.  So if we went the route that you're suggesting,
>> Typed Racket might serve the "what invariants should I help
>> programmers that read my code be aware of?" role, but we'd have to
>> take out the optimizer, and the claims that if Typed Racket tells you
>> something, then you know it to be true (modulo the extensive caveats
>> about bugs in TR, Racket, GCC, Linux, Intel, etc).  I don't think
>> that's the right trade to make.
> (I don't really get what you're saying here at all, but I also think
> it isn't really an argument against my argument.)
> But I'll note that you forgot perl in your list. I'm sure it is used
> in the build process of one of those tools that we rely on.
> Everything is hopeless.
> Robby
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