how to call a function from C
Hi, In Rcpp, we now have a "Function" class to encapsulate functions (they cover all three kinds, but this may change).
Just a note on that: there is probably no hurry to do so. rpy2 is also having CLOSXP, BUILTINSXP, and SPECIALSXP represented as one function-like class and seems to be behave reasonably while a lot of other things seem more urgent to sort out.
To call the function, what we do is generate a call with the function as the first node and then evaluate the call. SEXP stats = PROTECT( R_FindNamespace( mkString( "stats") ) ); SEXP rnorm = PROTECT( findVarInFrame( stats, install( "rnorm") ) ) ; SEXP call = PROTECT( LCONS( rnorm, CONS( ScalarInteger(10), CONS(ScalarReal(0), R_NilValue ) ) ) ); SEXP res = PROTECT( eval( call , R_GlobalEnv ) ); UNPROTECT(4) ; return res ; It works, but I was wondering if there was another way. I've seen applyClosure, but I'm not sure I should attempt to use it or if using a call like above is good enough.
Using R_tryEval() will let you evaluate an expression in a given environment, as well as capture an eventual error occurring during its evaluation (and translate it as an exception).
Romain
PS: using Rcpp's C++ classes you would express the code above as :
Environment stats("package:stats") ; Function rnorm = stats.get(
"rnorm" ) return rnorm( 10, 0.0 ) ;
Feel free to snoop in rpy2's rpy/rinterface/rinterface.c and look for
"do_try_eval". The behavior looks very similar, the above snippet in
rpy2 would write like:
from rpy2.robjects.packages import importr
stats = importr('stats')
stats.rnorm(10, 0.0)
-- Romain Francois Professional R Enthusiast +33(0) 6 28 91 30 30 http://romainfrancois.blog.free.fr |- http://tr.im/KfKn : Rcpp 0.7.2 |- http://tr.im/JOlc : External pointers with Rcpp `- http://tr.im/JFqa : R Journal, Volume 1/2, December 2009