It doesn't work (see the open bugs about it), it's not a GC and we don't work on it, see [https://github.com/nim-lang/RFCs/issues/177](https://github.com/nim-lang/RFCs/issues/177)
You're better off understanding Nim's memory management, why you cannot interface with Flex/Bison in the way you do and pick a different, real GC. Like the default one. I'll announce once `--gc:arc` is ready for a test drive.
