I have to write extensions to R regularly.
One of them was an interface to a mysql database on a
different computer. The best way to do that is to have
something like
mysql<-function (dbname, host = "zap", user = "nobody",
password = "ok")
{
handle <<- .RC("mysqlconnect", c(host, user, password,
dbname))
}
and
query<-function (cmd)
{
.RC("mysqlquery", handle, cmd)
}
In other words, my mysql (written in C) functions return a true R object.
The .RC function above simply calls the C funtion, passing R objects as
arguments and returns the R object created within the C function.
I think that R should give the ability to write C functions that build
R objects. Eventually, it would be best to have an API to standardize
the process of building R object too...
I'd like to see .RC added to the standard R distribution. Right now, I'm
applying my patch every time I upgrade R. Here is my diff
diff -r R-0.63/src/main/dotcode.c R-0.63.orig/src/main/dotcode.c
264,286d263
< SEXP do_dotRCode(SEXP call, SEXP op, SEXP args, SEXP env)
< {
< DL_FUNC fun;
< char buf[128], *p, *q, *vmax;
< SEXP retval;
<
< vmax = vmaxget();
< op = CAR(args);
< if (!isString(op)) errorcall(call,"function name must be a
string\n");
<
< /* make up load symbol & look it up */
< p = CHAR(STRING(op)[0]);
< q = buf; while ((*q = *p) != '\0') { p++; q++; }
<
< if (!(fun=R_FindSymbol(buf))) errorcall(call,
< "C-R function not in load table\n");
<
< retval=fun(args);
<
< vmaxset(vmax);
< return retval;
< }
<
969c946
< }
---> }
diff -r R-0.63/src/main/names.c R-0.63.orig/src/main/names.c
497d496
< {".RC", do_dotRCode, 0, 1, -1,
PP_FOREIGN},
diff -r R-0.63/src/main/names.h R-0.63.orig/src/main/names.h
128d127
< SEXP do_dotRCode(SEXP, SEXP, SEXP, SEXP);
If it is of interest, I could also provide the module that implements
the mysql interface.
Many thanks.
--
Jean Meloche
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