Type propagation proposal

[Marco Antoniotti]

> On Dec 22, 2015, at 08:26 , james anderson <james.anderson at setf.de> wrote:
> 
> good morning;
> 
>> On 2015-12-21, at 20:15, Attila Lendvai <attila at lendvai.name> wrote:
>> 
>> i wrote up some ideas here:
>> 
>> https://github.com/cffi/cffi/wiki/Type-propagation-proposal
>> 
>> you're invited to comment/edit it.
> 
> 
> [transported from otherwise private correspondence…]
> 
>> On 2015-12-22, at 00:16, Attila Lendvai <attila at lendvai.name> wrote:
>> 
>> hello,
>> 
>> […]
>> 
>>> the question is, did you consider using declarations and environments?
>>> i have found the sbcl implementation of those to be quite serviceable and i
>>> would expect it to provide all of the definition and access facilities which
>>> type-based operations could require.
>> 
>> as this is CFFI it should be portable, but i'm willing to give this up
>> if sane implementations can be made to work. there's an issue already
>> with portable access to the environment, but that has been dealt with
>> already.

I beg to differ.  There is NO code out there that correctly and portably has access to “the environment”.  I.e., at the level of CLtL2 Chapter 8.5.

>> do you think this could be implemented portably in a sane way? if so
>> maybe we should do that, but i never used user declarations.
> 
> i have never tried to validate my particular current use of the declaration facilities against some implementation other than sbcl, but i recall using them in lispworks, allegro and even mcl and see that ccl appears to implement them as well.
> the are cltl2 rather than ansi, but as they expose something which any implementation must already implement, they are a reasonable expectation.

Alas, they are not.  At this point only Allegro offers a working (and incomprehensibly non-cltl2-compliant - cfr., the return values order) version.  CMUCL and CCL do a reasonable job as does LW.

SBCL has lost SB-CLTL2 in the most recent (Mac) version.

ABCL’s maintainers are on record (personal communication :) :) :) ) as being ready to provide CLtL2 Chapter 8.5 functions “Very Soon Now”(TM).

I cannot say anything for ECL, CLISP or other implementations at this point.

> for sbcl i recall to need only to include :sb-cltl2 as an asdf dependency.

See above.

> the mechanism is pretty much transparent as to what the declaration can carry-
> that is, subject to scope and extent requirements, you can do pretty much whatever you want.

If it worked.

Having said that, I point you guys to CLAST: http://clast.sourceforge.net; any help is welcome, especially in lobbying the implementors to support CLtL2 Chapter 8.5.

I would like to have you note that CLAST constructs a “source level” AST for CL code, and that the PARSE-FORM generic function is the “form-level” hook to actually write an extension for CFFI definition forms.

Cheers

--
Marco Antoniotti