R devel - Apr 2007 - evaluation in unattached namespace

Hi,

I recently discovered this buglet in lattice: If lattice is _not_
attached, I get
> lattice::dotplot(~1:10)
Error in eval(expr, envir, enclos) : could not find function "bwplot"

This happens because of this:
> lattice:::dotplot.formula
function (x, data = NULL, panel = "panel.dotplot", ...)
{
    ocall <- ccall <- match.call()
    ccall$data <- data
    ccall$panel <- panel
    ccall[[1]] <- as.name("bwplot")
    ans <- eval.parent(ccall)
    ans$call <- ocall
    ans
}
<environment: namespace:lattice>

That is, ccall is eval()-ed in the global environment where bwplot is
not visible. While this example is somewhat silly, similar things
happen when I try to import lattice from another package.

Are there any simple alternatives? I tried

    ccall[[1]] <- as.name("lattice::bwplot")

but that didn't work either.

-Deepayan

On 4/26/2007 7:39 PM, Deepayan Sarkar wrote:
> Hi,
> 
> I recently discovered this buglet in lattice: If lattice is _not_
> attached, I get
> 
>> lattice::dotplot(~1:10)
> Error in eval(expr, envir, enclos) : could not find function
"bwplot"
> 
> This happens because of this:
> 
>> lattice:::dotplot.formula
> function (x, data = NULL, panel = "panel.dotplot", ...)
> {
>     ocall <- ccall <- match.call()
>     ccall$data <- data
>     ccall$panel <- panel
>     ccall[[1]] <- as.name("bwplot")
>     ans <- eval.parent(ccall)
>     ans$call <- ocall
>     ans
> }
> <environment: namespace:lattice>
> 
> That is, ccall is eval()-ed in the global environment where bwplot is
> not visible. While this example is somewhat silly, similar things
> happen when I try to import lattice from another package.
> 
> Are there any simple alternatives? I tried
> 
>     ccall[[1]] <- as.name("lattice::bwplot")
> 
> but that didn't work either.
One way would be to create a new environment with the caller's 
environment as the parent, and put a copy of bwplot in it, i.e. 
something like the following untested code:

  function (x, data = NULL, panel = "panel.dotplot", ...)
  {
      ocall <- ccall <- match.call()
      ccall$data <- data
      ccall$panel <- panel
      ccall[[1]] <- as.name("bwplot")
      evalenv <- new.env(parent = parent.frame())
      assign("bwplot", bwplot, envir=evalenv)
      ans <- eval(ccall, envir=evalenv)
      ans$call <- ocall
      ans
  }

Duncan Murdoch

On 4/26/07, Duncan Murdoch <murdoch at stats.uwo.ca>
wrote:
> On 4/26/2007 7:39 PM, Deepayan Sarkar wrote:
> > Hi,
> >
> > I recently discovered this buglet in lattice: If lattice is _not_
> > attached, I get
> >
> >> lattice::dotplot(~1:10)
> > Error in eval(expr, envir, enclos) : could not find function
"bwplot"
> >
> > This happens because of this:
> >
> >> lattice:::dotplot.formula
> > function (x, data = NULL, panel = "panel.dotplot", ...)
> > {
> >     ocall <- ccall <- match.call()
> >     ccall$data <- data
> >     ccall$panel <- panel
> >     ccall[[1]] <- as.name("bwplot")
> >     ans <- eval.parent(ccall)
> >     ans$call <- ocall
> >     ans
> > }
> > <environment: namespace:lattice>
> >
> > That is, ccall is eval()-ed in the global environment where bwplot is
> > not visible. While this example is somewhat silly, similar things
> > happen when I try to import lattice from another package.
> >
> > Are there any simple alternatives? I tried
> >
> >     ccall[[1]] <- as.name("lattice::bwplot")
Seth suggested

ccall[[1]] <- quote(lattice::bwplot)

which makes more sense and seems to work too.

-Deepayan