R devel - Apr 2011 - anyway to get R unevaluated expr independent on arguments

Hi there,

Suppose the cmd is "a<-3", I can parse the cmd sexp with
R_ParseVector and eval it. My question is - is it possible to parse a cmd like
"a <- ?", afterwards evaluation will give corresponding result
depend on different argument? In other words, '?' is just a placeholder.

Thanks.

Xin


	[[alternative HTML version deleted]]

On Apr 7, 2011, at 5:18 PM, Zheng, Xin (NIH) [C] wrote:
> Hi there,
> 
> Suppose the cmd is "a<-3", I can parse the cmd sexp with
R_ParseVector and eval it. My question is - is it possible to parse a cmd like
"a <- ?", afterwards evaluation will give corresponding result
depend on different argument? In other words, '?' is just a placeholder.
> 
Well, you can use a dummy symbol and replace it later, e.g. parse "a <-
`*dummy*`" and then before you evaluate you simply replace all occurrences
of the "*dummy*" symbol with any value you want.

That said, we are in a functional language, so you can actually do it more
natively by using a closure like "function(.var1){ a <- .var1 }"  -
that saves you the substitution part and is more clean.

Cheers,
Simon