All of your logic is sound, except that I think your understanding of functional programming is a bit too extreme. In the real world functional programming, just like object-oriented, or imperative programming is about mindset and how you approach the problem. You can still write programs in the spirit of functional programming while modifying application state.

In fact, you have to modify application state to actually do anything. The Haskell guys will tell you their programs are 'pure' because they wrap all of their state changes in a monad. However, their programs still do interact with the outside world. (Otherwise what is the point!)

Functional programming emphasis "no side effects" when it makes sense. However, to do real-world programming, like you said, you do need to modify the state of the world. (For example, responding to events, writing to disk, and so on.)

For more information on asynchronous programming in functional languages, I strongly urge you to look into F#'s Asynchronous Workflows programming model. It allows you to write functional programs while hiding all the messy details of thread transition within a library. (In a manner very similar to Haskell style monads.)

If the 'body' of the thread simply computes a value, then spawning multiple threads and having them compute values in parallel is still within the functional paradigm.

All of your logic is sound, except that I think your understanding of functional programming is a bit too extreme. In the real world functional programming, just like object-oriented, or imperative programming is about mindset and how you approach the problem. You can still write programs in the spirit of functional programming while modifying application state.

In fact, you have to modify application state to actually do anything. The Haskell guys will tell you their programs are 'pure' because they wrap all of their state changes in a monad. However, their programs still do interact with the outside world. (Otherwise what is the point!)

Functional programming emphasis "no side effects" when it makes sense. However, to do real-world programming, like you said, you do need to modify the state of the world. (For example, responding to events, writing to disk, and so on.)

For more information on asynchronous programming in functional languages, I strongly urge you to look into F#'s Asynchronous Workflows programming model. It allows you to write functional programs while hiding all the messy details of thread transition within a library. (In a manner very similar to Haskell style monads.)

If the 'body' of the thread simply computes a value, then spawning multiple threads and having them compute values in parallel is still within the functional paradigm.