This module supplies a method for writing
This moulde gives the highest performance, but requires many instance definitions. The
instances can be generated using Derive: http://community.haskell.org/~ndm/derive/.
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.Uniplate.Operations
- plate :: from -> Type from to
- plateSelf :: to -> Type to to
- (|+) :: Biplate item to => Type (item -> from) to -> item -> Type from to
- (|-) :: Type (item -> from) to -> item -> Type from to
- (|*) :: Type (to -> from) to -> to -> Type from to
- (||+) :: Biplate item to => Type ([item] -> from) to -> [item] -> Type from to
- (||*) :: Type ([to] -> from) to -> [to] -> Type from to
- plateProject :: Biplate item to => (from -> item) -> (item -> from) -> from -> Type from to
The main combinator used to start the chain.
The following rule can be used for optimisation:
plate Ctor |- x == plate (Ctor x)
The field to the right may contain the target.
The field to the right does not contain the target.
The field to the right is a list of types which may contain the target
The field to the right is a list of the type of the target
Write an instance in terms of a projection/injection pair. Usually used to define instances for abstract containers such as Map:
instance Biplate (Map.Map [Char] Int) Int where biplate = plateProject Map.toAscList Map.fromDistinctAscList
Because we know that Uniplate operations will not change the keys,
we can use the
fromDistictAscList function to reconstruct it.