Marcel,
On Aug 20, 2009, at 8:41 , MarcelK wrote:
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));
Scrap that - you're allocating data and in the next line you're
discarding it?!?
data = findVar(install("x"), rho);
Just add
if (TYPEOF(data) == PROMSXP)
data = eval(data, rho);
Cheers,
Simon
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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http://www.nabble.com/Problem-using-findVar%28-%29-in-combination-with-R%27s-lazy-evaluation-tp25061253p25061253.html
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