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
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