(Disclaimer: I've never programmed Haskell or used GHC outside of Xmonad) I'm pretty sure they use a M:N language-thread to OS-thread system. So they need to d

(Disclaimer: I've never programmed Haskell or used GHC outside of Xmonad) I'm pretty sure they use a M:N language-thread to OS-thread system. So they need to decide what thread to put "on" an OS-thread at any given time.