Haskell for simulating multilane traffic circle?

Question

It was hard for me to come up with a real-world example for a concurrency:

Imagine the above situation, where there are many lanes, many junctions and a great amount of cars. Besides, there is a human factor.

The problem is a hard research area for traffic engineers. When I investigated it a some time ago, I noticed that many models failed on it. When people are talking about functional programming, the above problem tends to pop up to my mind.

Can you simulate it in Haskell? Is Haskell really so concurrent? What are the limits to parallelise such concurrent events in Haskell?

Answer 1

I'm not sure what the question is exactly. Haskell 98 doesn't specify anything for concurrency. Specific implementations, like GHC, provide extensions that implement parallelism and concurrency.

To simulate traffic, it would depend on what you needed out of the simulation, e.g. if you wanted to track individual cars or do it in a general statistical way, whether you wanted to use ticks or a continuous model for time, etc. From there, you could come up with a representation of your data that lent itself to parallel or concurrent evaluation.

GHC provides several methods to leverage multiple hardware execution units, ranging from traditional semaphores and mutexes, to channels with lightweight threads (which could be used to implement an actor model like Erlang), to software transactional memory, to pure functional parallel expression evaluation, with strategies, and experimental nested data parallelism.

So yes, Haskell has many approaches to parallel execution that could certainly be used in traffic simulations, but you need to have a clear idea of what you're trying to do before you can choose the best digital representation for your concurrent simulation. Each approach has its own advantages and limits, including learning curve. You may even learn that concurrency is overkill for the scale of your simulations.