how to call a function from C

On 1/14/10 1:16 PM, Romain Francois wrote:

On 01/14/2010 12:42 PM, Laurent Gautier wrote:

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).

Sure. I did not want to over-complicate the question.

I'm currently reviewing tryEval and its underlying R_TopLevelExec which
does not give me enough : when the error occurs, it'd be useful that the
function returns the condition object instead of NULL.

I possibly went the same path, and ended with R_tryEval. When looking at
it, I could not figure out any way to get what I wanted outside using
"geterrmessage" in base.
The error string is in the variable errbuf (in src/main/error.c), with
no obvious route to access it (and if truly no route, this might be
something missing from the R C-API).

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:p/

I meant "do_eval_expr".

from rpy2.robjects.packages import importr
stats = importr('stats')
stats.rnorm(10, 0.0)

nice