interpretDsl.purs

import Control.Monad.Free (Free, liftF, foldFree)
import Effect (Effect)
import Effect.Console (log)

leftImpl ∷ State → State
leftImpl (State s) =
  case s.direction of
    North → State s { direction = West }
    South → State s { direction = East }
    East  → State s { direction = North }
    West  → State s { direction = South }

interpretDsl ∷ Dsl ~> Effect
interpretDsl = foldFree morph
  where
    morph :: DslF ~> Effect
    morph (Left state next) = do
      log $ show s1  --write to console
      pure $ next s1 --return our value inside of Effect
      where
        s1 = leftImpl state --get the new State of our rover