{-# Language LambdaCase #-}
module Assignment where

import Chi

subst :: Variable -> Exp -> Exp -> Exp
subst var e = \case
  Apply e1 e2 -> Apply (subst var e e1) (subst var e e2)
  Lambda x e' -> Lambda x $ if var /= x then (subst var e e') else e'
  Var x -> if var == x then e else Var x
  Const c es -> Const c $ map (subst var e) es
  Rec x e' -> Rec x $ if var /= x then (subst var e e') else e' 
  Case e' branches -> Case (subst var e e') $ map substBr branches
    where
      substBr :: Br -> Br
      substBr (Branch c vs e') = Branch c vs $ if var `notElem` vs then (subst var e e') else e'

eval' :: Exp -> Reader (Map Variable Exp) Exp
eval' = undefined

eval :: Exp -> Exp
eval = undefined

main :: IO ()
main = getLine >>= print . eval . parse