The VM monad is essentially a state monad, modifying the store. Besides returning pure values, various primitive effects may occur, such as printing characters or failing with an error message.

The alloc function allocate a fresh location on the heap.

The emptyLoc function removes the data stored at a given location. This corresponds, for instance, to emptying an MVar.

The freshThreadId function returns a previously unallocated ThreadId.

The finishThread function kills the thread with the specified ThreadId.

The lookupHeap function returns the data stored at a given heap location, if there is any.

The mainTid constant is the ThreadId of the main process.

The readChar and printChar functions are the primitive counterparts of getChar and putChar in the VM monad.

The updateHeap function overwrites a given location with new data.

The updateSoup function updates the process associated with a given ThreadId.

The Effect type contains all the primitive effects that are observable on the virtual machine.

The roundRobin scheduler provides a simple round-robin scheduler.

The singleThreaded scheduler will never schedule forked threads, always scheduling the main thread. Only use this scheduler if your code is not concurrent.

The Executable type class captures all the different types of operations that can be executed in the VM monad.

The runIOSpec function is the heart of this library. Given the scheduling algorithm you want to use, it will run a value of type IOSpec f a, returning the sequence of observable effects together with the final store.

The evalIOSpec function returns the effects a computation yields, but discards the final state of the virtual machine.

The execIOSpec returns the final Store after executing a computation.

Beware: this function assumes that your computation will succeed, without any other visible Effect. If your computation reads a character from the teletype, for instance, it will return an error.