R-alpha: Re: R-beta: ?faq example of scoping

[Luke Tierney]

Robert Gentleman wrote:
> 
>  I like Thomas' example. Kurt can you include it in the FAQ. 
>  
>  Recently I have been doing a lot of programming that has required either
>  optimization or zero-finding. Unfortunately most of the functions need
>  some arguments to be optimized over and have other parameters that depend on
>  the data but are fixed with respect to optimization. With R scoping rules
>  this is a trivial problem; simply make up the function with the required
>  definitions in the same environment and scoping takes care of it. With
>  Splus my solution has been to add an extra parameter to the function and
>  to the optimizer to pass in these extras. That's fine for optimizers I 
>  write myself but it doesn't work for the builtin ones. Fortunately I haven't
>  yet found a one-d problem that some thought and bisection won't take care
>  of.
>  
>  robert
>  

There might also be some use for a clean dynamic scoping mechanism to
to make it easier to make things like the minimizers in optimize.c
reentrant.  In 0.49 at least they use a static variable, and I think
things would go bad if they were called recursively. THis may not be
likely for a minimizer, but it would be very reasonable for an
integrator. You could save previous values of the globals on the C
stack, but with the need to provide protection for non-local exits on
errors this can get messy. A dynamic binding mechanism, preferably
with a separate name space like dynamic-bind stuff in Scheme, would
make this easier.

luke




-- 
Luke Tierney
University of Minnesota                      Phone:           612-625-7843
School of Statistics                         Fax:             612-624-8868
206 Church Street                            email:      luke@stat.umn.edu
Minneapolis, MN 55455 USA                    WWW:  http://www.stat.umn.edu
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