policy.hs

type Policy = State -> State

type Demand = State -> State

type Observation = (Demand, State)

eval :: State -> Policies -> Demands -> [State]
eval = ... 

observations :: State -> State -> [Observation]
observations = ...

s0 :: State
s0 = ...

policies :: Policies
policies = ...

simulate :: Demands -> [Observation]
simulate demands = 
  let 
    run state demandSample = 
      let 
        state_series = eval state policies demandSample
      in zipWith observations state_series (tail state_series) 
  in concat (map (run s0) demands `using` parList rdeepseq)