It's worth noting that the IO monad implementation is very much compiler magic and can't be done in library level haskell. Evaluation order without IO/ST is und

It's worth noting that the IO monad implementation is very much compiler magic and can't be done in library level haskell. Evaluation order without IO/ST is undefined in Haskell. This is similar to write barriers, you need a magic primop to specify external data dependencies. Without that magic the compiler may inline everything, drop the 'uselss' state token and happily move your buffer freeing before the allocation - or drop it entirely. Alternatively you could mark every function as noinline and end up with fantastically slow code.