On 02/05/2011 3:21 PM, Hadley Wickham wrote:
Hi all,
What's the preferred way of capturing the expression representing the
contents of a function?
* body(write.csv) gives me a braced expression
* body(write.csv)[-1] gives me a mangled call
* as.list(body(write.csv)[-1]) gives me a list of calls
* as.expression(as.list(body(write.csv)[-1])) is what I want but seems
like too much work
Any suggestions?
The body of a function isn't an expression, it's a language object. A
language object is represented internally as a pairlist, while an
expression is represented as a generic vector, i.e. the thing that
list() gives.
Your 1st try gives you the language object.
The other ones only work when the body consists of a call to `{`, as the
body of most complex functions does, but not for simple ones like
f <- function(x) 2*x
So I would say your question should be: "What's the best way to
construct an expression vector s.t. evaluating its elements in order is
like evaluating the body of a function?"
And the answer to that is something like
body2expr <- function(f) {
body <- body(f)
if (typeof(body) == "language" && identical(body[[1]], quote(`{`)))
as.expression(as.list(body[-1]))
else as.expression(body)
}
Duncan Murdoch
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