“The process has forked…” Error while using tm package in R

问题

I installed the tm package in R to do some text mining analysis. After creating a corpus I wanted to use the tm_map() function, which throws the following error message:

The process has forked and you cannot use this CoreFoundation functionality safely. You MUST exec().Break on 

Anybody an idea why this message turns up?

Here's more code for clarification:

> require(tm)
Lade nötiges Paket: tm
> a <-Corpus(VectorSource(chi2014_df$text))
> a
A corpus with 70 text documents
> a <-tm_map(a,tolower)
The process has forked and you cannot use this CoreFoundation functionality safely. You MUST exec().
Break on 

I'm using R 3.0.1 GUI 1.61 Snow Leopard build (6492) on OSX 10.7.5

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来源：https://stackoverflow.com/questions/18688599/the-process-has-forked-error-while-using-tm-package-in-r