R help - Apr 2012 - deferred call

I must admit I'm a little ashamed to have been using R for so long,
and still lack a sound understanding of deferred calls, eval, deparse,
substitute, and friends.

I'm attempting to make a deferred call to a function which has default
arguments in the following way:

call.foo <- function(f) {
    x <- f()
}

x <- 1:10
f <- function(x=x) { x^2 }
call.foo(f)

However, I'm getting the error:
Error in x^2 : 'x' is missing

Is there a common R idiom for calling 'formals' on the function, and
then grabbing the named default arguments from the enclosing frame?

I naively thought that since function 'f' was defined w/ a default
argument of 'x' and x is defined in the same envir as the function
itself, that the call would succeed.

-Whit

On Wed, Apr 11, 2012 at 10:17 PM, Whit Armstrong
<armstrong.whit at gmail.com> wrote:
> I must admit I'm a little ashamed to have been using R for so long,
> and still lack a sound understanding of deferred calls, eval, deparse,
> substitute, and friends.
>
> I'm attempting to make a deferred call to a function which has default
> arguments in the following way:
>
> call.foo <- function(f) {
> ? ?x <- f()
> }
>
> x <- 1:10
> f <- function(x=x) { x^2 }
> call.foo(f)
>
> However, I'm getting the error:
> Error in x^2 : 'x' is missing
>
> Is there a common R idiom for calling 'formals' on the function,
and
> then grabbing the named default arguments from the enclosing frame?
>
> I naively thought that since function 'f' was defined w/ a default
> argument of 'x' and x is defined in the same envir as the function
> itself, that the call would succeed.
>
f <- function(x=x) x^2 is an endless recursion.  Try

 f <- function(x.=x) { x^2 }

(note the dot)

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