Pass unevaluated commands to a function in R

I am a bit of an R novice, and I am stuck with what seems like a simple problem, yet touches pretty deep questions about how and when things get evaluated in R.

I am using Rserve quite a bit; the typical syntax to get things evaluated remotely is a bit of a pain to type repeatedly:

RSeval(connection, quote(try(command)))

So I would like a function r which does the same thing with just the call:

r(command)

My first, naive, bound to fail attempt involved:

r <- function(command) {
    RSeval(c, quote(try(command)))
}

You've guessed it: this sends, literally, try(command) to my confused Rserve daemon. I want comma开发者_运维技巧nd to be partially evaluated, if that makes any sense -- i.e. replaced by what I typed as an argument, but without evaluating it locally.

I looked for solutions to this, browsed throught the documentation for quote, substitute, eval, call, etc.. but I was not able to find something that worked. Either command gets evaluated locally, or not at all.

This is not a big problem, I can type the whole damn quote(try()) thing all the time; but at this point I am mostly curious as to how to get this to work!

EDIT: More explanations as to what I want to do.

• In the text above, command is meant to be a call do a function, ideally -- i.e., not a character string. Something like a <- 3 or assign("a", 3) rather than "a<-3" or quote(a<-3). I believe that this is part of what makes this tricky. It seems really hard to tell R not to evaluate this locally, but only send it literally. Basically I would like my function to be a bit like quote(), which does not evaluate its argument.
• Some explanation about my intentions. I wish to use Rserve frequently to pass commands to a remote R daemon. The commands would be my own (or my colleagues) and the daemon protected by firewall and authentication (and would not be run as root) -- so there is no worry of malicious commands being passed.
• To be perfectly honest, this is not a big issue, and I would be pretty happy to always use the RSeval(c, quote(try())). At this point I see this more like an interesting inquiry into the subleties of R :-)

You probably want to use the substitute command, it can give you the argument unevaluated that you can build into the call.

I'm not sure if I understood you correctly - would eval(parse(text = command)) do the trick? Notice that command is a character, so you can easily pass it as a function argument. If I'm getting the point...

Anyway, evaluating user-specified commands is potentially malicious, therefore not recommended. You should either install AppArmor and tweak it (which is not an easy one), or drop the whole evaluation thing...