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.
Moduleuniplate-1.6.13Haskell2010
Data.Generics.Uniplate
DEPRECATED Use Data.Generics.Uniplate.Operations 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- Packageuniplate-1.6.13
- Exports13
- LanguageHaskell2010
- LicenceBSD-3-Clause
- SourceUniplate.hs
The Class
The standard Uniplate class, all operations require this
Methods
uniplate :: UniplateType onThe underlying method in the class
uniplate (Add (Val 1) (Neg (Val 2))) = ([Val 1, Neg (Val 2)], \[a,b] -> Add a b) uniplate (Val 1) = ([] , \[] -> Val 1 )
The Operations
Queries
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 = [i | Val i <- universe x]Transformations
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 = xMonadic variant of transform
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.
Monadic variant of rewrite
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.
Monadic variant of descend
Others
Return all the contexts and holes.
propUniverse x = universe x == map fst (contexts x)
propId x = all (== x) [b a | (a,b) <- contexts x]The one depth version of contexts
propChildren x = children x == map fst (holes x)
propId x = all (== x) [b a | (a,b) <- holes x]Perform a fold-like computation on each value, technically a paramorphism