[R] from character string to function body?

[Sundar Dorai-Raj]

Atte Tenkanen said the following on 7/7/2007 8:41 AM:
> Dear R users,
> 
> I wonder if it is possible to form a function from a character string. Here is an example:
> 
> 
>> x=3
>> `-`(`+`(`^`(x,3),`^`(x,2)),1) # Here is my function evaluated.
> [1] 35
> 
>> V=list("`-`","(","`+`","(","`^`","(","x",",",3,")",",","`^`","(","x",",",2,")",")",",",1,")") # Here I construct the string, it could be vector as well?
>>
>> S=noquote(paste(V,collapse=""))
>>
>> S
> [1] `-`(`+`(`^`(x,3),`^`(x,2)),1) # Here is the same as a character string.
> 
> Now I'd like to create a function using this string, something like this, but of course, this doesn't work:
> 
> S=as.expression(S)
> 
> F1<-function(x){S}
> 
> Is there some way to do this?
> 
> Cheers,
> 
> Atte Tenkanen
> University of Turku, Finland
> 
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How about:

V <- 
list("`-`","(","`+`","(","`^`","(","x",",",3,")",",","`^`","(","x",",",2,")",")",",",1,")") 
# Here I construct the string, it could be vector as well?
S <- paste(V, collapse = "")

F1 <- function(x) {}
body(F1) <- parse(text = S)
F1(3)
# [1] 35
F1(2)
# [1] 11

HTH,

--sundar