1{-# LANGUAGE CPP, MultiParamTypeClasses, DeriveGeneric, DeriveDataTypeable #-}
2module Plates where
3
4#if !(MIN_VERSION_base(4,8,0))
5import Control.Applicative
6#endif
7import Control.Lens
8import GHC.Generics
9import Data.Data
10
11data Expr = Var Int | Pos Expr String | Neg Expr | Add Expr Expr deriving (Eq,Ord,Show,Read,Generic,Data,Typeable)
12data Stmt = Seq [Stmt] | Sel [Expr] | Let String Expr deriving (Eq,Ord,Show,Read,Generic,Data,Typeable)
13
14instance Plated Expr where
15  plate _ (Var x  ) = pure (Var x)
16  plate f (Pos x y) = Pos <$> f x <*> pure y
17  plate f (Neg x  ) = Neg <$> f x
18  plate f (Add x y) = Add <$> f x <*> f y
19
20instance Plated Stmt where
21  plate f (Seq xs)  = Seq <$> traverse f xs
22  plate _ (Sel xs)  = pure (Sel xs)
23  plate _ (Let x y) = pure (Let x y)
24
25exprs :: Traversal' Stmt Expr
26exprs f (Seq xs)  = Seq <$> traverse (exprs f) xs
27exprs f (Sel xs)  = Sel <$> traverse f xs
28exprs f (Let x y) = Let x <$> f y
29