Re: [Rd] R-devel Digest, Vol 83, Issue 2

From: Duncan Murdoch <murdoch_at_stats.uwo.ca>
Date: Sat, 02 Jan 2010 19:23:19 -0500

On 02/01/2010 6:35 PM, Laurent Gautier wrote:
> On 1/2/10 11:41 PM, Romain Francois wrote:

>> On 01/02/2010 11:12 PM, Duncan Murdoch wrote:
>>> On 02/01/2010 3:16 PM, Laurent Gautier wrote:
>>>> On 1/2/10 8:53 PM, Duncan Murdoch wrote:
>>>>> Simon Urbanek wrote:
>>>>>> On Jan 2, 2010, at 12:17 PM, Laurent Gautier wrote:
>>>>>>
>>>>>>> On 1/2/10 5:56 PM, Duncan Murdoch wrote:
>>>>>>>> On 02/01/2010 11:36 AM, Laurent Gautier wrote:
>>>>>>>>> [Disclaimer: what is below reflects my understanding from reading
>>>>>>>>> the
>>>>>>>>> R source, others will correct where deemed necessary]
>>>>>>>>>
>>>>>>>>> On 1/2/10 12:00 PM, r-devel-request_at_r-project.org wrote:
>>>>>>> (...)
> (...)
>>> I don't think I would want to review such a patch (I don't know the
>>> memory manager well, I don't know that there is really a case where it
>>> matters enough to be worth doing), so I'd say if you don't get a message
>>> from a core member volunteering to do so, you should assume it won't be
>>> accepted. But that doesn't mean you shouldn't write the code for your
>>> own internal use and edification, and if you can put together a demo
>>> that shows it really makes a big difference in a realistic situation,
>>> you might get a different response.
>>>
>>> Duncan Murdoch

>> From what I understand, this has little to do with the memory manager,
>> and resumes to the simple problem "how to remove an object from a list".
> 
> I would generalize even further, up to: "how to make a tail recursion 
> into an interation" (and that often boils down to writing a for loop - 
> little edification to get from it, I suppose... one probably wants to 
> write it to see it included).

Just one followup: as Luke mentioned, I was wrong, it isn't really a tail recursion (which is why gcc didn't optimize it away).

Duncan Murdoch

> 
> I see below that you are living up to the enthusiasm claimed, and had a 
> shot at it (and even did benchmark to demonstrate the expected benefit - 
> impressive).
> 
> Let's see what happens with it...
> 
> 
> L.
> 

>> Something like this, using the amazing inline and inspect packages:
>>

>> require( inline )
>> require( inspect )
>>

>> remover <- cfunction(signature( list = "language", object =
>> "environment" ), '
>> if( !isNull( list ) ){
>> SEXP x = list ;
>> SEXP y ;
>> while( CAR(x) != object && CADR(x) != R_NilValue ){
>> y = x ;
>> x = CDR(x) ;
>> }
>> if( CAR(x) == object ) SETCDR(y, CDR(x) ) ;
>> }
>> return list ;
>> ', Rcpp=FALSE, verbose=FALSE )
>>

>> e <- new.env()
>> call <- call( "foo", e, e, 1:10, 3 )
>> call
>> # inspect( call )
>> result <- remover( call ,e )
>> result
>> # inspect( result )
>>

>> gives this :
>>

>> foo(10, <environment>, 0, <environment>, 1)
>> @0x9f4e0d0 06 LANGSXP [NAM(2)]
>> @0x9f4e204 01 SYMSXP [] "foo"
>> @0xa907b78 14 REALSXP [NAM(2)] (len=1, tl=1763713056)
>> @0x9f4d564 04 ENVSXP [NAM(1)]
>> FRAME:
>> @0x9e94a10 00 NILSXP [MARK,NAM(2)]
>> ENCLOS:
>> @0x9eb7b4c 04 ENVSXP [MARK,NAM(2),GP(0x8000)]
>> HASHTAB:
>> @0x9e94a10 00 NILSXP [MARK,NAM(2)]
>> @0xa907b58 14 REALSXP [NAM(2)] (len=1, tl=1936941344)
>> @0x9f4d564 04 ENVSXP [NAM(1)]
>> FRAME:
>> @0x9e94a10 00 NILSXP [MARK,NAM(2)]
>> ENCLOS:
>> @0x9eb7b4c 04 ENVSXP [MARK,NAM(2),GP(0x8000)]
>> HASHTAB:
>> @0x9e94a10 00 NILSXP [MARK,NAM(2)]
>> @0xa907b38 14 REALSXP [NAM(2)] (len=1, tl=543908709)
>> NULL
>> ==================
>> foo(10, 0, <environment>, 1)
>> @0x9f4e0d0 06 LANGSXP [NAM(2)]
>> @0x9f4e204 01 SYMSXP [] "foo"
>> @0xa907b78 14 REALSXP [NAM(2)] (len=1, tl=1763713056)
>> @0xa907b58 14 REALSXP [NAM(2)] (len=1, tl=1936941344)
>> @0x9f4d564 04 ENVSXP [NAM(2)]
>> FRAME:
>> @0x9e94a10 00 NILSXP [MARK,NAM(2)]
>> ENCLOS:
>> @0x9eb7b4c 04 ENVSXP [MARK,NAM(2),GP(0x8000)]
>> HASHTAB:
>> @0x9e94a10 00 NILSXP [MARK,NAM(2)]
>> @0xa907b38 14 REALSXP [NAM(2)] (len=1, tl=543908709)
>> NULL
>>
>>
>>

>> so it boils down to this as a replacement to RecursiveRelease :
>>

>> /**
>> * Removes the first instance of object with the list
>> */
>> static SEXP RemoveFromList( SEXP object, SEXP list){
>> if( !isNull( list ) ){
>> SEXP x = list ;
>> SEXP y ;
>> while( CAR(x) != object && CADR(x) != R_NilValue ){
>> y = x ;
>> x = CDR(x) ;
>> }
>> if( CAR(x) == object ) SETCDR(y, CDR(x) ) ;
>> }
>> return list ;
>> }
>>
>>

>> Romain
>>
>>
> 
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