[jeremyjh]

Haskell's scheduler preempts on memory allocation. Memory allocation is ubiquitous in Haskell; the example you are giving cannot really be written in Haskell as values are immutable. You could try to do something with IORef and bang patterns to avoid thunks being allocated but you are now in a very tiny corner case, much smaller than the surface area of NIFs that can cause you problems in both Erlang and Haskell.