On Nov 30, 2009, at 16:07 , Guillaume Yziquel wrote:
Simon Urbanek a écrit :
And it goes then to my other question: How can you pass to eval a
LANGSXP where the CAR is an *anonymous* function, no SYMSXP
involved?
You just pass it as value of the call. I suspect the reason it
doesn't work is in your code, not in the facility (note that the
link above is useless since the construction is mystery - if you
were constructing it right, it would work ;)).
Small example:
SEXP myEval(SEXP FN, SEXP first_arg) {
return eval(LCONS(FN, CONS(first_arg, R_NilValue)), R_GlobalEnv);
}
> .Call("myEval",function(x) x + 1, 10)
[1] 11
In the eval function in eval.c, you have:
case LANGSXP:
if (TYPEOF(CAR(e)) == SYMSXP)
/* This will throw an error if the function is not found
*/
PROTECT(op = findFun(CAR(e), rho));
else
PROTECT(op = eval(CAR(e), rho));
So imagine you have a LANGSXP whose CAR is a CLOSXP, the execution
goes into the last line of the code snippet above.
And re-entring eval with a CLOSXP, the code goes into
tmp = R_NilValue; /* -Wall */
#ifdef Win32
/* This is an inlined version of Rwin_fpreset (src/gnuwin/extra.c)
and resets the precision, rounding and exception modes of a
ix86
fpu.
*/
__asm__ ( "fninit" );
#endif
R_Visible = TRUE;
switch (TYPEOF(e)) {
case NILSXP:
case LISTSXP:
case LGLSXP:
case INTSXP:
case REALSXP:
case STRSXP:
case CPLXSXP:
case RAWSXP:
case S4SXP:
case SPECIALSXP:
case BUILTINSXP:
case ENVSXP:
case CLOSXP:
case VECSXP:
case EXTPTRSXP:
so PROTECT(op = eval(CAR(e), rho)) evaluates to R_NilValue.
Nope, it simply evaluates to itself (with ref count increased) - see
tmp = e; ..; return(tmp).
I figured out that's why evaluating a LANGSXP with CAR a CLOSXP
simply fails.
Wrong ;). A closure is a constant like any other object so it
evaluates to itself.
Cheers,
Simon
I'll have a look at the code snippet you gave, since I do not
understand why it doesn't fail the same way mine does.
Thanks a lot.
--
Guillaume Yziquel
http://yziquel.homelinux.org/
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