R devel - Feb 2011 - as.list(subclassed function) -> cannot coerce type 'closure' to vector of type 'list'

I was looking for all the glm-related 'family' functions
in stats using the following predicate that returns TRUE
for any function whose first argument is called "link".
   is.family <- function(object) is.function(object) &&
            identical(names(as.list(object))[1], "link")

It threw an error when applied to SSfol
   > is.family(SSfol)
   Error in as.vector(x, "list") :
     cannot coerce type 'closure' to vector of type 'list'
but works when I unclass SSfol
   > is.family(unclass(SSfol))
   [1] FALSE

It looks like as.list fails on any function that is assigned
a class:
   > as.list(function(x)x+1)
   $x
   
   
   [[2]]
   x + 1

   > as.list(structure(function(x)x+1, class="unrecognized class
name"))
   Error in as.vector(x, "list") :
     cannot coerce type 'closure' to vector of type 'list'

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

For this application I would use names(formals(object)) to extract the
formal arguments.

luke

On Mon, 7 Feb 2011, William Dunlap wrote:
> I was looking for all the glm-related 'family' functions
> in stats using the following predicate that returns TRUE
> for any function whose first argument is called "link".
>   is.family <- function(object) is.function(object) &&
>            identical(names(as.list(object))[1], "link")
>
> It threw an error when applied to SSfol
>   > is.family(SSfol)
>   Error in as.vector(x, "list") :
>     cannot coerce type 'closure' to vector of type 'list'
> but works when I unclass SSfol
>   > is.family(unclass(SSfol))
>   [1] FALSE
>
> It looks like as.list fails on any function that is assigned
> a class:
>   > as.list(function(x)x+1)
>   $x
>
>
>   [[2]]
>   x + 1
>
>   > as.list(structure(function(x)x+1, class="unrecognized class
name"))
>   Error in as.vector(x, "list") :
>     cannot coerce type 'closure' to vector of type 'list'
>
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
-- 
Luke Tierney
Statistics and Actuarial Science
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:      luke at stat.uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu

This is because there is an as.list.function, but your classed object 
does not inherit from 'function'.

However, I think coercing to a list is S-like, and in R we have 
formals() and body(), and I think you want the former.

Seems this was a late 2008 change: maybe the author can tell us why it 
was done?

On Mon, 7 Feb 2011, William Dunlap wrote:
> I was looking for all the glm-related 'family' functions
> in stats using the following predicate that returns TRUE
> for any function whose first argument is called "link".
>   is.family <- function(object) is.function(object) &&
>            identical(names(as.list(object))[1], "link")
>
> It threw an error when applied to SSfol
>   > is.family(SSfol)
>   Error in as.vector(x, "list") :
>     cannot coerce type 'closure' to vector of type 'list'
> but works when I unclass SSfol
>   > is.family(unclass(SSfol))
>   [1] FALSE
>
> It looks like as.list fails on any function that is assigned
> a class:
>   > as.list(function(x)x+1)
>   $x
>
>
>   [[2]]
>   x + 1
>
>   > as.list(structure(function(x)x+1, class="unrecognized class
name"))
>   Error in as.vector(x, "list") :
>     cannot coerce type 'closure' to vector of type 'list'
>
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
-- 
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