MTL-style circuit simulator

After the first attempt at making a very side-effectful circuit simulator, and then an ambitious attempt at making it pure, I was reminded of a middle ground, using a pattern common in production Haskell code. It is called MTL-style effects, and it is a specific type of final tagless encoding. The idea is that we first find a set of operations that our circuit simulator needs to support. Drawing this boundary well requires some experience and taste. Then we encode that limited set of operations into a type class. Here’s one way to do it. In[1]: class CircuitOperations m where make_wire :: m Wire get_signal :: Wire -> m Signal set_signal :: Wire -> Signal -> m () add_action :: Wire -> m () -> m () after_delay :: Int -> m () -> m () get_time :: m Int probe_output :: String -> m () propagate :: m () Having read the previous article, these operations should sound familiar. I’m sure it’s possible to create a better set of operations, but this will suffice to illustrate the point. (Continue…