R help - Jan 2008 - question from Blue book

Hi R people:
  
 On page 235 of the Blue Book (Becker, Chambers, and Wilks), there is a
"compose2" function.
  
 compose2 <- function(f,g) {
 gg <- substitute(g1(x))
 print(gg)
 gg[[1]] <- g
 ff <- substitute(f1(y))
 print(ff)
 ff[[1]] <- f
 ff[[2]] <- gg
 print(ff)
 fun <- function(x){ NULL }
 fun[[2]] <- ff
 fun
}

 However, when I run this function using sum and log (as in the example), I get
the following error:
  
 Error in fun[[2]] <- ff : object of type 'closure' is not
subsettable
>
 Has anyone else run into this, please?
 Or is this a merely an issue with a dated concept, please?
  
 Thanks in advance,
 Sincerely,
 Erin Hodgess
  
 mailto: hodgess@gator.uhd.edu
  
 
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On Thu, 3 Jan 2008, hodgess wrote:
>
>    Hi R people:
>
> On page 235 of the Blue Book (Becker, Chambers, and Wilks), there is a
"compose2" function.
>
> compose2 <- function(f,g) {
> gg <- substitute(g1(x))
> print(gg)
> gg[[1]] <- g
> ff <- substitute(f1(y))
> print(ff)
> ff[[1]] <- f
> ff[[2]] <- gg
> print(ff)
> fun <- function(x){ NULL }
> fun[[2]] <- ff
> fun
> }
>
> However, when I run this function using sum and log (as in the example), I
get the following error:
>
> Error in fun[[2]] <- ff : object of type 'closure' is not
subsettable
>>
> Has anyone else run into this, please?
> Or is this a merely an issue with a dated concept, please?
The implementation of functions is different in S and in R.  You need to 
use body() and formals() in R (functions which did not exist in S).
>From memory, an n-arg function in S has n+1 components, the arguments plus 
the body.
> Thanks in advance,
> Sincerely,
> Erin Hodgess
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595