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Description | |||||||||||||||||||||||||||
RECOMMENDATION Use Data.Generics.UniplateStr instead. 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 Expr type as below: 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 universe is more appropriate. children = fst . uniplate | |||||||||||||||||||||||||||
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 = transform 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 | |||||||||||||||||||||||||||
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 transform is more appropriate, but rewrite can give better compositionality. Given two single transformations f and g, you can construct f mplus g which performs both rewrites until a fixed point. | |||||||||||||||||||||||||||
rewriteM :: (Monad m, Uniplate on) => (on -> m (Maybe on)) -> on -> m on | |||||||||||||||||||||||||||
Monadic variant of rewrite | |||||||||||||||||||||||||||
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 | |||||||||||||||||||||||||||
Others | |||||||||||||||||||||||||||
contexts :: Uniplate on => on -> [(on, on -> on)] | |||||||||||||||||||||||||||
Return all the contexts and holes. propUniverse x = universe x == map fst (contexts x) propId x = all (== x) [b a | (a,b) <- contexts x] | |||||||||||||||||||||||||||
holes :: Uniplate on => on -> [(on, on -> on)] | |||||||||||||||||||||||||||
The one depth version of contexts propChildren x = children x == map fst (holes x) propId x = all (== x) [b a | (a,b) <- holes x] | |||||||||||||||||||||||||||
para :: Uniplate on => (on -> [r] -> r) -> on -> r | |||||||||||||||||||||||||||
Perform a fold-like computation on each value, technically a paramorphism | |||||||||||||||||||||||||||
Produced by Haddock version 0.8 |