I am working on creating an operational semantics interpreter in haskell for an assignment but am not sure how to implement the semantic functions for statements. The semantinc functions i need to have implemented are assignment, seq, if, and while. The code is represented below. The current semantic functions for statements is found at the bottom of the program.

module Interpreter ( emptyState, sStep ) where import Prelude hiding (lookup) import While type Z = Integer -- | In lecture, we represented the state as a function. Here we represent state -- as an association list instead. type State = [(Var,Z)] -- | The empty state contains no bindings for any variables---it as an empty -- association list. emptyState :: State emptyState = [] -- | 'lookup' finds a variable in the current state. Note that it is a partial -- function---we don't gracefully handle use of an undefined variable. lookup :: Var -> State -> Z lookup v [] = error $ "undefined variable " ++ show v lookup v ((v',n):vs) | v' == v = n | otherwise = lookup v vs -- | 'extend' adds or replaces a binding in the current state. To avoid an -- exploding association list, we prune any previous binding for @v@. extend :: State -> Var -> Z -> State extend vs v n = (v,n) : filter (\(v', _) -> v' /= v) vs -- | The semantic function for arithmetic expressions aSem :: Aexp -> State -> Z aSem (Const x) _ = x aSem (Var v) s = lookup v s aSem (Add a1 a2) s = aSem a1 s + aSem a2 s aSem (Sub a1 a2) s = aSem a1 s - aSem a2 s aSem (Mul a1 a2) s = aSem a1 s * aSem a2 s -- | The semantic function for boolean expressions bSem :: Bexp -> State -> Bool bSem BTrue _ = True bSem BFalse _ = False bSem (Eq a1 a2) s = aSem a1 s == aSem a2 s bSem (Le a1 a2) s = aSem a1 s <= aSem a2 s bSem (Not b) s = not (bSem b s) bSem (And b1 b2) s = bSem b1 s && bSem b2 s -- | The semantic function for statements should be added here sStep :: Stm -> State -> State sStep Skip s = s sStep (Out _) s = s sStep _ _ = error "sStep: you need to fill in the missing cases in Interpreter.hs"