uniplate-1.6.12: Help writing simple, concise and fast generic operations.

Safe Haskell | None
Language | Haskell98

Data.Generics.Uniplate.Direct

Contents

- The Combinators
- Orphan instances

Description

This module supplies a method for writing `Uniplate` and `Biplate` instances. 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 `Map` or `Set` from the `containers` package, use `plateProject`.

This module provides a few monomorphic instances of `Uniplate` / `Biplate` 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. Consider `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, such as `Biplate a [a]` and `Biplate a a`, but take care to avoid overlapping instances.

Synopsis

- 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

# Documentation

module Data.Generics.Uniplate.Operations

# The Combinators

plate :: 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)

plateSelf :: to -> Type to to #

Used for `Biplate` definitions where both types are the same.

(|+) :: Biplate item to => Type (item -> from) to -> item -> Type from to #

The field to the right may contain the target.

(|-) :: Type (item -> from) to -> item -> Type from to #

The field to the right does not contain the target.

(|*) :: Type (to -> from) to -> to -> Type from to #

The field to the right is the target.

(||+) :: Biplate item to => Type ([item] -> from) to -> [item] -> Type from to #

The field to the right is a list of types which may contain the target

(||*) :: Type ([to] -> from) to -> [to] -> Type from to #

The field to the right is a list of the type of the target

plateProject :: Biplate item to => (from -> item) -> (item -> from) -> from -> Type from to #

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

# Orphan instances

Uniplate Bool # |
Methods uniplate :: Bool -> (Str Bool, Str Bool -> Bool) # descend :: (Bool -> Bool) -> Bool -> Bool # descendM :: Monad m => (Bool -> m Bool) -> Bool -> m Bool #
Uniplate Char # |
Methods uniplate :: Char -> (Str Char, Str Char -> Char) # descend :: (Char -> Char) -> Char -> Char # descendM :: Monad m => (Char -> m Char) -> Char -> m Char #
Uniplate Double # |
Methods uniplate :: Double -> (Str Double, Str Double -> Double) # descend :: (Double -> Double) -> Double -> Double # descendM :: Monad m => (Double -> m Double) -> Double -> m Double #
Uniplate Float # |
Methods uniplate :: Float -> (Str Float, Str Float -> Float) # descend :: (Float -> Float) -> Float -> Float # descendM :: Monad m => (Float -> m Float) -> Float -> m Float #
Uniplate Int # |
Methods uniplate :: Int -> (Str Int, Str Int -> Int) # descend :: (Int -> Int) -> Int -> Int # descendM :: Monad m => (Int -> m Int) -> Int -> m Int #
Uniplate Integer # |
Methods uniplate :: Integer -> (Str Integer, Str Integer -> Integer) # descend :: (Integer -> Integer) -> Integer -> Integer # descendM :: Monad m => (Integer -> m Integer) -> Integer -> m Integer #
Uniplate () # |
Methods uniplate :: () -> (Str (), Str () -> ()) # descend :: (() -> ()) -> () -> () # descendM :: Monad m => (() -> m ()) -> () -> m () #
Uniplate [Char] # |
Methods uniplate :: [Char] -> (Str [Char], Str [Char] -> [Char]) # descend :: ([Char] -> [Char]) -> [Char] -> [Char] # descendM :: Monad m => ([Char] -> m [Char]) -> [Char] -> m [Char] #
Uniplate (Ratio Integer) # |
Methods uniplate :: Ratio Integer -> (Str (Ratio Integer), Str (Ratio Integer) -> Ratio Integer) # descend :: (Ratio Integer -> Ratio Integer) -> Ratio Integer -> Ratio Integer # descendM :: Monad m => (Ratio Integer -> m (Ratio Integer)) -> Ratio Integer -> m (Ratio Integer) #
Biplate [Char] Char # |
Methods biplate :: [Char] -> (Str Char, Str Char -> [Char]) # descendBi :: (Char -> Char) -> [Char] -> [Char] # descendBiM :: Monad m => (Char -> m Char) -> [Char] -> m [Char] #
Biplate (Ratio Integer) Integer # |
Methods biplate :: Ratio Integer -> (Str Integer, Str Integer -> Ratio Integer) # descendBi :: (Integer -> Integer) -> Ratio Integer -> Ratio Integer # descendBiM :: Monad m => (Integer -> m Integer) -> Ratio Integer -> m (Ratio Integer) #
Biplate [Char] [Char] # |
Methods biplate :: [Char] -> (Str [Char], Str [Char] -> [Char]) # descendBi :: ([Char] -> [Char]) -> [Char] -> [Char] # descendBiM :: Monad m => ([Char] -> m [Char]) -> [Char] -> m [Char] #
Biplate (Ratio Integer) (Ratio Integer) # |
Methods biplate :: Ratio Integer -> (Str (Ratio Integer), Str (Ratio Integer) -> Ratio Integer) # descendBi :: (Ratio Integer -> Ratio Integer) -> Ratio Integer -> Ratio Integer # descendBiM :: Monad m => (Ratio Integer -> m (Ratio Integer)) -> Ratio Integer -> m (Ratio Integer) #