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Description | |||||||||||||||||||||||||

This is the main Uniplate module, which defines all the essential operations in a Haskell 98 compatible manner. Most functions have an example of a possible use for the function.
To illustate, I have used the data Expr = Val Int | Neg Expr | Add Expr Expr | |||||||||||||||||||||||||

Synopsis | |||||||||||||||||||||||||

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The Class | |||||||||||||||||||||||||

type UniplateType on = on -> ([on], [on] -> on) | |||||||||||||||||||||||||

The type of replacing all the children of a node Taking a value, the function should return all the immediate children of the same type, and a function to replace them. | |||||||||||||||||||||||||

class Uniplate on where | |||||||||||||||||||||||||

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The Operations | |||||||||||||||||||||||||

Queries | |||||||||||||||||||||||||

universe :: Uniplate on => on -> [on] | |||||||||||||||||||||||||

Get all the children of a node, including itself and all children. universe (Add (Val 1) (Neg (Val 2))) = [Add (Val 1) (Neg (Val 2)), Val 1, Neg (Val 2), Val 2] This method is often combined with a list comprehension, for example: vals x = [Val i | i <- universe x] | |||||||||||||||||||||||||

children :: Uniplate on => on -> [on] | |||||||||||||||||||||||||

Get the direct children of a node. Usually using children = fst . | |||||||||||||||||||||||||

Transformations | |||||||||||||||||||||||||

transform :: Uniplate on => (on -> on) -> on -> on | |||||||||||||||||||||||||

Transform every element in the tree, in a bottom-up manner. For example, replacing negative literals with literals: negLits = trasform f where f (Neg (Lit i)) = Lit (negate i) f x = x | |||||||||||||||||||||||||

transformM :: (Monad m, Uniplate on) => (on -> m on) -> on -> m on | |||||||||||||||||||||||||

Monadic variant of transform
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rewrite :: Uniplate on => (on -> Maybe on) -> on -> on | |||||||||||||||||||||||||

Rewrite by applying a rule everywhere you can. Ensures that the rule cannot be applied anywhere in the result: propRewrite r x = all (isNothing . r) (universe (rewrite r x)) Usually | |||||||||||||||||||||||||

rewriteM :: (Monad m, Uniplate on) => (on -> m (Maybe on)) -> on -> m on | |||||||||||||||||||||||||

Monadic variant of rewrite
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descend :: Uniplate on => (on -> on) -> on -> on | |||||||||||||||||||||||||

Perform a transformation on all the immediate children, then combine them back. This operation allows additional information to be passed downwards, and can be used to provide a top-down transformation. | |||||||||||||||||||||||||

descendM :: (Monad m, Uniplate on) => (on -> m on) -> on -> m on | |||||||||||||||||||||||||

Monadic variant of descend
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Others | |||||||||||||||||||||||||

contexts :: Uniplate on => on -> [(on, on -> on)] | |||||||||||||||||||||||||

Return all the contexts and holes. This operation is only occasionally useful. propUniverse x = universe x == map fst (contexts x) propId x = all (== x) [b a | (a,b) <- contexts x] | |||||||||||||||||||||||||

fold :: Uniplate on => (on -> [r] -> r) -> on -> r | |||||||||||||||||||||||||

Perform a fold on each value | |||||||||||||||||||||||||

Produced by Haddock version 0.8 |