Creating functions with eval(parse()) containing numeric vectors - r

Question

I have several functions as strings which contain a lot of numeric vectors in the form of
c(1,2,3) , with three fixed values each (3D-coordinates). See test_string below as a small example. I can create a working function test_fun using eval and parse, but there is a problem:
I need these vectors to be recognized as one input, i.e. as double[3] and not as language with the parts 'c' (symbol), 1 (double[1]), 2 (double[1]) and 3 (double[1]). Check this code to see what I mean:
test_string <- "function(x) \n c(1,2,3)*x"
test_fun <- eval(parse(text = test_string))
test_fun(2)
#[1] 2 4 6 <- it's working
View(list(test_fun)) # see 'type' column
str(body(test_fun)[[2]])
# language c(1, 2, 3) <- desired output here: num [1:3] 1 2 3
str(body(test_fun)[[2]][[1]])
# symbol c
Is there an easy solution that works on the full string? I would be very happy to learn about this! If necessary I could also change the code in the function which creates these function strings when the substrings are concatenated with paste("function(x) \n ","c(1,2,3)","*x",sep = "").
Edit: I did a mistake in the 'View' and 'desired output' line. It is now correct.

Answer 1

I think I found a solution that works for me. If there is a more elegant solution, please let me know!
I go recursively through the function body and evaluate the parts which are numerical vectors a second time (like #Allan Cameron suggested, thanks!). Here is the function:
evalBodyParts <- function(fun_body){
for (i in 1:length(fun_body)){ #i=2
if (typeof(fun_body[[i]])=="language" &&
typeof(fun_body[[i]][[1]])=="symbol" && fun_body[[i]][[1]]=="c"){
#if first element is symbol 'c' the whole list is only num [1:3] here
fun_body[[i]] <- eval(fun_body[[i]])
} else {
if(typeof(fun_body[[i]])=="language"){
fun_body[[i]] <- evalBodyParts(fun_body=fun_body[[i]])
}
}
}
return(fun_body)
}
To do a quick example which is a bit more complex than the one in the main question above, let me show you the following.
Before:
test_string <- paste("function(x) \n ","c(1,2,3)","*x","+c(7,8,9)",sep = "")
test_fun <- eval(parse(text = test_string))
test_fun(2) # it's working
# [1] 9 12 15
str(body(test_fun)[[2]][[2]])
# language c(1, 2, 3)
str(body(test_fun)[[3]])
# language c(7, 8, 9)
After:
body(test_fun) <- evalBodyParts(fun_body=body(test_fun))
test_fun(2) # it is still working
# [1] 9 12 15
str(body(test_fun)[[2]][[2]])
# num [1:3] 1 2 3
str(body(test_fun)[[3]])
# num [1:3] 7 8 9