[Haskell-cafe] Why is TChan GHC specific?

[Edward Amsden]

I'm currently just getting into playing around with concurrency in
haskell, primarily because I find STM intriguing. In looking through
the docs I noticed that the transactional channels are GHC specific.
http://hackage.haskell.org/packages/archive/stm/2.1.1.2/doc/html/Control-Concurrent-STM-TChan.html

I dug around the wiki and Google but I couldn't find the reason for this.