talk.otl

CougarCS meeting 2014-10-23

R-extensions and embedding R in Perl

====

R's C API is documented at <http://cran.r-project.org/doc/manuals/r-release/R-exts.html>

Top of your C file
	; #include <R.h>
	; #include <Rinternals.h>

SEXP
	s-expressions
		like in Lisp
			: (cdr (cdr (cdr '(A B C D))))
			> (D)
		R's design inspired by Scheme
	hold all variable types
		http://cran.r-project.org/doc/manuals/r-release/R-exts.html#Details-of-R-types
		: SEXPTYPE	R equivalent
		:===================================================
		: REALSXP	numeric with storage mode double
		: INTSXP	integer
		: CPLXSXP	complex
		: LGLSXP	logical
		: STRSXP	character
		: VECSXP	list (generic vector)
		: LISTSXP	pairlist
		: DOTSXP	a ‘…’ object
		: NILSXP	NULL
		: SYMSXP	name/symbol
		: CLOSXP	function or function closure
		: ENVSXP	environment
	refer to variables as SEXP
		: SEXP convolve2(SEXP a, SEXP b) {
		:    /* ... */
		: }
		; ft=c
	you can find out the type of a SEXP variable
		: SEXP a;
		:
		: switch( TYPEOF(a) ) {
		:     case REALSEXP:
		:         /* double */
		:     case INTSEXP:
		:         /* integer */
		:     case STRSEXP:
		:         /* strings */
		: }
	Two ways of calling
		.C("c_fn", arg1, arg2, arg3)
		.External("ext_fn", arg1, arg2, arg3)
		difference
			.C passes in each SEXP argument separately
			.External passes in all the arguments as a single SEXP variable
				a list of all the arguments