Getting the parse tree for a predefined function in R

Question

I feel as if this is a fairly basic question, but I can't figure it out.

If I define a function in R, how do I later use the name of the function to get its parse tree. I can't just use substitute as that will just return the parse tree of its argument, in this case just the function name.

For example,

> f <- function(x){ x^2 }
> substitute(f)
f

How should I access the parse tree of the function using its name? For example, how would I get the value of substitute(function(x){ x^2 }) without explicitly writing out the whole function?

Answer 1

I'm not exactly sure which of these meets your desires:

 eval(f)
#function(x){ x^2 }

 identical(eval(f), get("f"))
#[1] TRUE
 identical(eval(f), substitute( function(x){ x^2 })  )
#[1] FALSE

 deparse(f)
#[1] "function (x) " "{"             "    x^2"       "}"            

 body(f)
#------
{
    x^2
}
#---------

eval(parse(text=deparse(f)))
#---------
function (x) 
{
    x^2
}
#-----------

 parse(text=deparse(f))
#--------
expression(function (x) 
{
    x^2
})
#--------

 get("f")
# function(x){ x^2 }

The print representation may not display the full features of the values returned.

 class(substitute(function(x){ x^2 }) )
#[1] "call"
 class( eval(f) ) 
#[1] "function"