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
|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|
|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
|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|
|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|
|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|