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

Data.Generics.PlateDirect

Contents

Description

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

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
```

Synopsis

• module Data.Generics.Biplate
• 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

# The Combinators

plate :: from -> Type from toSource

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 toSource

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

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

The field to the right may contain the target.

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

The field to the right does not contain the target.

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

The field to the right is the target.

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

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

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

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