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{-# LANGUAGE MultiParamTypeClasses, DeriveGeneric, DeriveDataTypeable #-}
module Plates where
import Control.Lens
import GHC.Generics
import Data.Data
data Expr = Var Int | Pos Expr String | Neg Expr | Add Expr Expr deriving (Eq,Ord,Show,Read,Generic,Data)
data Stmt = Seq [Stmt] | Sel [Expr] | Let String Expr deriving (Eq,Ord,Show,Read,Generic,Data)
instance Plated Expr where
plate _ (Var x ) = pure (Var x)
plate f (Pos x y) = Pos <$> f x <*> pure y
plate f (Neg x ) = Neg <$> f x
plate f (Add x y) = Add <$> f x <*> f y
instance Plated Stmt where
plate f (Seq xs) = Seq <$> traverse f xs
plate _ (Sel xs) = pure (Sel xs)
plate _ (Let x y) = pure (Let x y)
exprs :: Traversal' Stmt Expr
exprs f (Seq xs) = Seq <$> traverse (exprs f) xs
exprs f (Sel xs) = Sel <$> traverse f xs
exprs f (Let x y) = Let x <$> f y
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