[Bioc-devel] Lazy evaluation and S4 methods

Hi everyone,

I'm trying to investigate lazy evaluation with S4, and specifically
the environment chain available for lookup when an S4 method is
evaluated.

With 'vanilla' R functions, we can write something like the following:

    lazy <- function(...) {
      call <- substitute(list(...))
      for (i in 2:length(call)) {
        eval(call[[i]])
      }
    }

and evaluation will succeed if this function is called by another function:

    f <- function() {
      var <- 10
      lazy(x = var)
    }

    f()

The evaluation of the symbol 'var' is able to find it in the 'f' environment.

    setClass("Lazy", list(data="list"))
    setGeneric("lazy", function(x, ...) standardGeneric("lazy"))
    setMethod("lazy", list(x="Lazy"), function(x, ...) {
      call <- substitute(list(...))
      for (i in 2:length(call)) {
        eval( call[[i]] )
      }
    })

    f <- function() {
      var <- new("Lazy", data=list(1))
      y <- 1
      cat("\n")
      lazy(var, a=y)
    }

    f()

gives ' Error in eval(expr, envir, enclos) : object 'y' not found '.
It seems like the S4 method is evaluated in an environment detached
from the scope of the caller (which is probably outlined in ?Methods,
but I am having trouble parsing everything in there).

My main question is -- is there a nice way to work around this, in a
way that is transparent to the user of a function?

Further motivation available in the GitHub issue for flowCore here:
https://github.com/RGLab/ncdfFlow/issues/31

Thanks,
Kevin