{-# LANGUAGE MultiParamTypeClasses #-} {- | This module supplies a method for writing 'Biplate' instances more easily. This module requires fewest extensions, highest performance, and most instance definitions. To take an example: > data Expr = Var Int | Pos Expr String | Neg Expr | Add Expr Expr > data Stmt = Seq [Stmt] | Sel [Expr] | Let String Expr > > instance Uniplate Expr where > uniplate (Var x ) = plate Var |- x > uniplate (Pos x y) = plate Pos |* x |- y > uniplate (Neg x ) = plate Neg |* x > uniplate (Add x y) = plate Add |* x |* y > > instance Biplate Expr Expr where > biplate = plateSelf > > instance Uniplate Stmt where > uniplate (Seq x ) = plate Seq ||* x > uniplate (Sel x ) = plate Sel ||+ x > uniplate (Let x y) = plate Let |- x |- y > > instance Biplate Stmt Stmt where > biplate = plateSelf > > instance Biplate Stmt Expr where > biplate (Seq x ) = plate Seq ||+ x > biplate (Sel x ) = plate Sel ||* x > biplate (Let x y) = plate Let |- x |* y -} module Data.Generics.PlateDirect( module Data.Generics.Biplate, -- * The Combinators plate, plateSelf, (|+), (|-), (|*), (||+), (||*) ) where import Data.Generics.Biplate import Data.Generics.PlateInternal import Data.Generics.Str import Data.Maybe type Type from to = (Str to, Str to -> from) -- | The main combinator used to start the chain. -- -- The following rule can be used for optimisation: -- -- > plate Ctor |- x == plate (Ctor x) plate :: from -> Type from to plate f = (Zero, \_ -> f) -- | The field to the right is the target. (|*) :: Type (to -> from) to -> to -> Type from to (|*) (xs,x_) y = (Two xs (One y),\(Two xs (One y)) -> x_ xs y) -- | The field to the right may contain the target. (|+) :: Biplate item to => Type (item -> from) to -> item -> Type from to (|+) (xs,x_) y = case biplate y of (ys,y_) -> (Two xs ys, \(Two xs ys) -> x_ xs (y_ ys)) -- | The field to the right /does not/ contain the target. (|-) :: Type (item -> from) to -> item -> Type from to (|-) (xs,x_) y = (xs,\xs -> x_ xs y) -- | The field to the right is a list of the type of the target (||*) :: Type ([to] -> from) to -> [to] -> Type from to (||*) (xs,x_) y = (Two xs (listStr y), \(Two xs ys) -> x_ xs (strList ys)) -- | The field to the right is a list of types which may contain the target (||+) :: Biplate item to => Type ([item] -> from) to -> [item] -> Type from to (||+) (xs,x_) y = case plateListDiff y of (ys,y_) -> (Two xs ys, \(Two xs ys) -> x_ xs (y_ ys)) where plateListDiff [] = plate [] plateListDiff (x:xs) = plate (:) |+ x ||+ xs -- | Used for 'PlayAll' definitions where both types are the same. plateSelf :: to -> Type to to plateSelf x = (One x, \(One x) -> x)