Just about this one some important term 'closure', hence I'm
modifying the subject.
Note we came here from my 2nd reason why I had added 'monoH.FC'
feature only for splinefun() and not for spline() :
- splinefun() is using's R feature of "(non-trivial) closure", i.e,
it returns a *function* containing its own state
-------------
Yes, there is some vagueness / ambiguity about how the term
"closure" is used within R documentation and teaching :
Yes, indeed, the term stems from lisp ("Scheme" more
specifically according to
https://en.wikipedia.org/wiki/Closure_(computer_programming) ,
but you should remember that R originally had been implemented
as a "lisp with S-syntax" (that's my paraphrasing), see
https://en.wikipedia.org/wiki/R_(programming_language)
and (in the box on the right hand side) its list of
"Influenced by" : Common Lisp, S, Scheme[2], XLispStat
and [2] is Ross Ihaka's famous Interface paper :
Ihaka, Ross (1998). R : Past and Future History (PDF) (Technical report).
Statistics Department, The University of Auckland, Auckland, New Zealand.
https://www.stat.auckland.ac.nz/~ihaka/downloads/Interface98.pdf
And that's the reason why typeof(f) for all functions 'f'
which are not primitive is "closure".
All such functions (i.e. *not* the primitives) have an
environment, as Mark Leeds explains, and what this means and
why this is very important is beyond 'R-help'.
Inside R's own C code, all such R functions are "closures", and
programmers (incl R corers) who think more about the low level
view of R objects would use the term like that ex
OTOH, Hadley Wickham has written a book "Advanced R" which has been
the best book about advanced R by far (in my view, notably
before it morphed (towards the 2nd edition) to use more and more
non-base R packages). There, he used "Closure" in a different,
stricter sense, starting the section 'Closures' with
βAn object is data with functions.
A closure is a function with data.β β John D. Cook
Now, most functions have only a "trivial environment" (my own
terminology, when I'm teaching "advanced R" courses/classes,
see https://github.com/mmaechler/ProgRRR/ for some teaching material)
"trivial environment" meaning that their environment is
- either the namespace belonging to the package the function is part of
- or .GlobalEnv { which is the same as globalenv() }
and most functions with non-trivial environment are just
"helper" functions defined inside other functions which are very
short lived (during the evaluation of the outer function's call).
Now the remaining few functions with non-trivial environments
that you see in "base R" are those returned by
splinefun(), approxfun(), ecdf(), or stepfun()
where the last two actually are implemented via approxfun().
-- -- --
I hope this has been useful "writeup" about
'closure' ..
Best,
Martin
Martin Maechler
ETH Zurich and R Core team
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
