{-# LANGUAGE MultiParamTypeClasses, TypeFamilies, FlexibleInstances #-}

module Fib.Kure where

import Control.Applicative

import Language.KURE
import Fib.AST

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-- | For this simple example, the context is always empty and 'Translate' always operates on 'Arith'
type TranslateA b = Translate () Maybe Arith b
type RewriteA = TranslateA Arith

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instance Term Arith where
  type Generic Arith = Arith

  numChildren (Lit _)   = 0
  numChildren (Add _ _) = 2
  numChildren (Sub _ _) = 2
  numChildren (Fib _)   = 1

instance Walker () Maybe Arith where

  childL n = lens $ \ c e -> case e of
                               Lit _      ->  empty
                               Add e1 e2  ->  case n of
                                                0 -> pure ((c,e1), \ e1' -> pure (Add e1' e2))
                                                1 -> pure ((c,e2), \ e2' -> pure (Add e1 e2'))
                                                _ -> empty
                               Sub e1 e2  ->  case n of
                                                0 -> pure ((c,e1), \ e1' -> pure (Sub e1' e2))
                                                1 -> pure ((c,e2), \ e2' -> pure (Sub e1 e2'))
                                                _ -> empty
                               Fib e1     ->  case n of
                                                0 -> pure ((c,e1), \ e1' -> pure (Fib e1'))
                                                _ -> empty

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