could not find function inside foreach loop

Question

I'm trying to use foreach to do multicore computing in R.

A <-function(....) {
    foreach(i=1:10) %dopar% {
    B()
    }
}

then I call function A in the console. The problem is I'm calling a function Posdef inside B that is defined in another script file which I source. I had to put Posdef in the list of export argument of foreach: .export=c("Posdef"). However I get the following error:

Error in { : task 3 failed - "could not find function "Posdef""

Why cant R find this defined function?

Answer 1

So I can reproduce this, for the curious:

require(doSNOW)
registerDoSNOW(makeCluster(5, type="SOCK"))
getDoParWorkers()
getDoParName()
getDoParVersion()

fib <- function(n) {
  if (n <= 1) { return(1) }
  return(fib(n-1) + fib(n-2))
}

my.matrix <- matrix(runif(2500, 10, 50), nrow=50)

calcLotsaFibs <- function() {
  result <- foreach(row.num=1:nrow(my.matrix), .export=c("fib", "my.matrix")) %dopar% {
    return(Vectorize(fib)(my.matrix[row.num,]))
  }
  return(result)
}

lotsa.fibs <- calcLotsaFibs()

I have been able to get around this by putting the function in another file and loading that file in the body of the foreach. You could also obviously move the function definition into the body of the foreach itself.

[EDIT -- I had previously suggested that perhaps .export doesn't work properly with function names, but was corrected below.]