From luke-tierney at uiowa.edu  Mon Apr 18 22:42:51 2011
From: luke-tierney at uiowa.edu (luke-tierney at uiowa.edu)
Date: Mon, 18 Apr 2011 15:42:51 -0500
Subject: [Rd] Tail Call Elimination?
In-Reply-To: <BANLkTinPucAOmqLBtZtLQ+YzQ7VsYmUT9A@mail.gmail.com>
References: <BANLkTim3Y+zfNBBjGTXE4PijRqv41Cs-nw@mail.gmail.com>
	<alpine.DEB.2.00.1104180941470.1955@luke-inspiron>
	<BANLkTinPucAOmqLBtZtLQ+YzQ7VsYmUT9A@mail.gmail.com>
Message-ID: <alpine.DEB.2.00.1104181542170.1955@luke-inspiron>

On Mon, 18 Apr 2011, Dominick Samperi wrote:

> On Mon, Apr 18, 2011 at 10:41 AM,  <luke-tierney at uiowa.edu> wrote:
>> The premise of your post is false: contrary to popular belief, R's
>> looping constructs are not particularly inefficient. Slowness of loops
>> relative to vectorized code comes from the cost of interpreting the
>> body of the loop. ?That exact same interpreter would be used to
>> interpret the bodies of functions used to express loops using
>> recursion, so it is not reasonable to expect this to improve
>> performance. In fact, due to the inefficiency of the current function
>> call mechanism in R, quite the opposite is true.
>>
>> As to the question: tail call optimization cannot be applied in R, at
>> least not in a simple way, because the semantics of R provide access
>> to the call stack via the sys.xyz functions and parent.frame and such.
>> It might be possible to make some semantic changes, such as only
>> guaranteeing access to the immediate caller, but there isn't much
>> point unless/until the performance of the function calling mechanism is
>> improved.
>>
>> Best,
>>
>> luke
>
> To what extent does the recently introduced byte-code compilation
> help here?

It can help quite a bit if the loop body is such that its evaluation
is dominated by interpreter overhead.  If the body involves calls to
computationally expensive fucntons then compiling the loop itself may
not help very much, but compiling those functions might.

Best,

luke

>
>> On Sun, 17 Apr 2011, Mohit Dayal wrote:
>>
>>> Dear R-programmers,
>>>
>>> I am trying to program a Newton-Raphson in R (yes, i will try GSL, not
>>> right
>>> now), and it would be a real boon if R had tail call elimination, so that
>>> a
>>> recursive program has a guarantee not to fail due to stack overflows,
>>> given
>>> how slow loops in R are. I did look at the documentation, but could not
>>> find
>>> a reason for it.
>>>
>>> Regards,
>>> Mohit Dayal
>>> Researcher
>>> Applied Statistics & Computing Lab
>>> ISB
>>>
>>> ? ? ? ?[[alternative HTML version deleted]]
>>>
>>> ______________________________________________
>>> R-devel at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>>
>>
>> --
>> Luke Tierney
>> Statistics and Actuarial Science
>> Ralph E. Wareham Professor of Mathematical Sciences
>> University of Iowa ? ? ? ? ? ? ? ? ?Phone: ? ? ? ? ? ? 319-335-3386
>> Department of Statistics and ? ? ? ?Fax: ? ? ? ? ? ? ? 319-335-3017
>> ? Actuarial Science
>> 241 Schaeffer Hall ? ? ? ? ? ? ? ? ?email: ? ? ?luke at stat.uiowa.edu
>> Iowa City, IA 52242 ? ? ? ? ? ? ? ? WWW: ?http://www.stat.uiowa.edu
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>

-- 
Luke Tierney
Statistics and Actuarial Science
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:      luke at stat.uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu


[Rd] Tail Call Elimination?
luke-tierney at uiowa.edu