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
To define instances for abstract data types, such as
Set from the
This module provides a few monomorphic instances of
for common types available in the base library, but does not provide any polymorphic
instances. Given only monomorphic instances it is trivial to ensure that all instances
are disjoint, making it easier to add your own instances.
When defining polymorphic instances, be carefully to mention all potential children.
Biplate Int (Int, a) - this instance cannot be correct because it will fail
to return both
Int values on
(Int,Int). There are some legitimate polymorphic instances,
Biplate a [a] and
Biplate a a, but take care to avoid overlapping instances.
- 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) Char where biplate = plateProject Map.toList Map.fromList
If the types ensure that no operations will not change the keys
we can use the
fromDistictAscList function to reconstruct the Map:
instance Biplate (Map.Map [Char] Int) Int where biplate = plateProject Map.toAscList Map.fromDistinctAscList