[Rcpp-devel] Trouble passing arguments to R functions that have been passed in (maybe)

[Anthony Lee]

Hello,

I'm quite new to Rcpp (and R in fact) and I'm having a little bit of 
trouble understanding what is going on in some of my code. I have 
written a fairly small example that exhibits the troublesome behaviour 
using inline (below). The code doesn't do anything interesting, but 
runCode() does cause a "memory not mapped" error. Other times I get an 
"unimplemented type 'NULL' in 'coerceToInteger'" error.

It seems to be the case that sometimes the values N and true do not make 
it back safely to R when calling bar within foo and get transformed into 
NULL or doubles, etc. I still have issues if I "PROTECT" their 
conversion to SEXP via wrap.

I know it is not particularly good to have C++ functions calling R 
functions that have been passed in, but this is a very useful feature 
for me and I have been very happy with Rcpp until this starting happening.

Any help on what mistake I've made would be greatly appreciated.

Thanks,
Anthony

Code: (note that removing X and Y seems to make the code more stable)

require(inline)

foo <- cxxfunction(
   signature(N_in = "numeric", n_in = "numeric", bar_in = "function"), 
body='
   BEGIN_RCPP
   int N = as<int>(N_in);
   int n = as<int>(n_in);
   Function bar(bar_in);
   IntegerMatrix A(N,n);
   GenericMatrix X(N,n);
   GenericMatrix Y(N,n);
   A(_,0) = seq_len(N-1);

   for (int i = 1; i < n; i++) {
     A(_,i) = as<IntegerVector>(bar(A(_,i-1),N,true));
   }

   return wrap(A);
   END_RCPP
   ', plugin = "Rcpp" )

translate <- function(size,cond,vs) {
   if (cond) {
     return((vs + 1) %% size)
   } else {
     return((vs - 1) %% size)
   }
}

bar <- function(vs,M,cond) {
   return(translate(size=M,cond=cond,vs=vs))
}

runCode <- function() {
   for (i in 1:5) {
     for (j in 1:10) {
       print(paste(i,j,sep=" "));
       B <- foo(i*100,j*100,bar);
     }
   }
}

# runCode()