-- Solver.hs
-- cleaned up with stylish-haskell (hackage)
-- and https://github.com/tibbe/haskell-style-guide
-- also, flatten is 'concat', I think

{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE MultiParamTypeClasses  #-}
{-# LANGUAGE ScopedTypeVariables    #-}

module Solver
    (Solver,State,Transition)
  where

class (Show t,Eq t) => Transition t where
    transition :: State s => s -> t -> s

class (Show s,Eq s) => State s where
    getPossibleTransitions :: Transition t => s -> [t]
    isStateValid :: s -> Bool
    isGoalState  :: s -> Bool

class (State s, Transition t) => Solver s t | s -> t where
    getPossibleNextStates :: s -> [s]
    getPossibleNextStates state =
       filter isStateValid (map transitionFunction possibleTransitions)
      where
       transitionFunction  = transition state :: t -> s
       possibleTransitions = getPossibleTransitions state

    isStateVisited        :: [s] -> s -> Bool
    isStateVisited visitedStates state =
       any (== state) visitedStates

    getNextFringeStates :: [s] -> [[s]]
    getNextFringeStates = map getPossibleNextStates