Hi All,
I have a few small questions about the usage of the C findVar( ) function
when used in C code called with '.Call'. In my case I create an R function
with an argument. This function calls some C code in which I use findVar( )
to retrieve the values from the argument. Ofcourse normally I would just
give the values as argument to .Call, but in my project I need to use
findVar for various reasons (can elaborate if needed, but it's not really
relevant..) Below is a small example of an R function and the C code in
which the problem shows: (skip to bold 'question' part if this is allready
known)
----------# R function #--------
f <- function(x) {
.Call("envtest", environment())
}
----------# C function #--------
SEXP envtest(SEXP rho) {
SEXP data;
PROTECT(data = allocVector(REALSXP, 1));
data = findVar(install("x"), rho);
UNPROTECT(1);
return(data);
}
----------# END #-----------
The result of this function is that it should print the contents of whatever
is passed to the function f(x). But when executing the function, the result
is:
> f(10)
<promise: 0x142db20>
Ofcourse this is due to lazy-evaluation as I've also read in the thread
http://www.nabble.com/confusion-about-evaluation.-to18561135.html#a18563086
here .
To 'fix' it, I would need to do 'something' with 'x', so changing the
function f() to:
f <- function(x) {
x = x
.Call("envtest", environment())
}
works as can be shown with:
> f(10)
[1] 10
----------
My question on this subject is, how can I work around this 'x = x' or other
similar statement (print(x) to prevent lazy-evaluation? To summarize, I
would like to use findVar to retrieve values from R objects which are given
as function arguments to the R-function and not to the C-function.
Other than the above question, I'd also like to know if findVar( ) by
default also checks parent environments (inherits argument?) when the object
can not be found in the given environment (if not, should I look into
passing the environment Hash etc?).
And, as a last question, how can I retrieve the value from the R-constant
'pi' using findVar? If I try this I receive the error "REAL can only be
applied to 'numeric' not a 'promise'".
Thank you for any solutions or insights in these subjects, if more details
are needed I'm happy to give them!
Marcel Kempenaar
----------------
> sessionInfo()
R version 2.9.1 (2009-06-26)
x86_64-pc-linux-gnu
locale:
LC_CTYPE=en_US.UTF-8;LC_NUMERIC=C;LC_TIME=nl_NL.UTF-8;LC_COLLATE=C;LC_MONETARY=C;LC_MESSAGES=en_US.UTF-8;LC_PAPER=nl_NL.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_US.UTF-8;LC_IDENTIFICATION=C
attached base packages:
[1] stats graphics grDevices utils datasets methods base
--
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