Proof of concept protection against free variables. The purpose is to avoid passing a function to a subprocess for parallel evaluation when that function depends on variables that are only available in the parent process.

prevent-free-vars.R

library(codetools)

getNonPackageVars <- function (pos=-1L, envir=as.environment(pos)) {
    npvarnames <- c()
    while (TRUE) {
        if (identical(envir, emptyenv()) ||
            identical(envir, .BaseNamespaceEnv)) {
            ## If we hit the empty env, then we started in a package
            ## namespace, so there are no non-package vars.
            return(character(0))
        }
        if (identical(envir, baseenv()))
        message("Looking in env: ", capture.output(print(envir)))
        npvarnames <- c(npvarnames, ls(envir=envir))
        if (identical(envir, globalenv())) {
            ## After we process the global env, we're done
            break()
        }
        envir <- parent.env(envir)            
    }
    unique(npvarnames)
}

getNonPackageFreeVars <- function (fun) {
    npvars <- getNonPackageVars(environment(fun))
    fun.freevars <- findGlobals(fun)
    intersect(fun.freevars, npvars)
}

do.call.if.ok <- function(what, ...) {
    what <- match.fun(what)
    badvars <- getNonPackageFreeVars(what)
    if (length(badvars) > 0) {
        stop("Function contains free variables: ", deparse(badvars))
    }
    do.call(what=what, ...)
}
x <- 5
okfunc <- function (a, b) a + b
freevarfunc <- function (a) a + x + y

getNonPackageFreeVars(okfunc)
getNonPackageFreeVars(freevarfunc)
getNonPackageFreeVars(rnorm)

do.call.if.ok(okfunc, list(a=1, b=2))
do.call.if.ok(freevarfunc, list(a=1))
do.call.if.ok(rnorm, list(10))