A few comments interspersed. On Mon, Dec 8, 2008 at 5:59 PM, Stavros Macrakis <[EMAIL PROTECTED]> wrote: > I've read in many places that R semantics are based on Scheme semantics. As > a long-time Lisp user and implementor, I've tried to make this more precise, > and this is what I've found so far. I've excluded trivial things that > aren't basic semantic issues: support for arbitrary-precision integers; > subscripting; general style; etc. I would appreciate corrections or > additions from more experienced users of R -- I'm sure that some of the > points below simply reflect my ignorance. > > ==Similarities to Scheme== > > R has first-class function closures. (i.e. correctly supports upward and > downward funarg). > > R has a single namespace for functions and variables (Lisp-1).
Environments can be used to create separate name spaces. R packages can use the NAMESPACE file to set up their own namespace. > > ==Important dissimilarities to Scheme (as opposed to other Lisps)== > > R is not properly tail-recursive. > > R does not have continuations or call-with-current-continuation or other > mechanisms for implementing coroutines, general iterators, and the like. > True although there is callCC but it just lets you jump right of a nested sequence of calls. > R supports keyword arguments. > > ==Similarities to Lisp and other dynamic languages, including Scheme== > > R is runtime-typed and garbage-collected. > > R supports nested read-eval-print loops for debugging etc. > > R expressions are represented as user-manipulable data structures. > > ==Dissimilarities to all (modern) Lisps, including Scheme== > > R has call-by-need, not call-by-object-value. Call by need? > > R does not have macros. You can create them. See: Programmer's Niche: Macros in R http://cran.r-project.org/doc/Rnews/Rnews_2001-3.pdf > > R objects are values, not pointers, so a<-1:10; b<-a; b[1]<-999; a[1] => > 999. Similarly, functions cannot modify the contents of their arguments. > a[1] is not 999 after the above completes (if that is what is meant by a[1] => 999): > a<-1:10; b<-a; b[1]<-999 > a [1] 1 2 3 4 5 6 7 8 9 10 > There is no equivalent to set-car!/rplaca (not even pairlists and > expressions). For example, r<-pairlist(1,2); r[[1]]<-r does not create a > circular list. And in general there doesn't seem to be substructure sharing > at the semantic level (though there may be in the implementation). > > R does not have multiple value return in the Lisp sense. You can do this: http://finzi.psych.upenn.edu/R/Rhelp02a/archive/36820.html > R assignment creates a new local variable on first assignment, dynamically. > So static analysis is not enough to determine variable reference (R is not > referentially transparent). Example: ff <- function(a){if (a) x<-1; x} ; > x<-99; ff(T) -> 1; ff(F) -> 99. > > In R, most data types (including numeric vectors) do not have a standard > external representation which can be read back in without evaluation. ??? > > R coerces logicals to numbers and numbers to strings. Lisps are stricter > about automatic type conversion -- except that false a.k.a. NIL == () in > Lisps other than Scheme. ______________________________________________ R-help@r-project.org mailing list 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.
