On Mon, 18 Apr 2011, Dominick Samperi wrote:
On Mon, Apr 18, 2011 at 10:41 AM, <luke-tier...@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
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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
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241 Schaeffer Hall email: l...@stat.uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
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--
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: l...@stat.uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
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