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Data.Generics.UniplateStr |
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Description |
RECOMMENDATION: 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
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Synopsis |
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The Class
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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.
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The standard Uniplate class, all operations require this.
| | Methods | | The underlying method in the class.
Given uniplate x = (cs, gen)
cs should be a Str on, constructed of Zero, One and Two,
containing all x's direct children of the same type as x. gen
should take a Str on with exactly the same structure as cs,
and generate a new element with the children replaced.
Example instance:
instance Uniplate Expr where
uniplate (Val i ) = (Zero , \Zero -> Val i )
uniplate (Neg a ) = (One a , \(One a) -> Neg a )
uniplate (Add a b) = (Two (One a) (One b), \(Two (One a) (One b)) -> Add a b)
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| | Instances | |
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Compatibility method, for direct users of the old list-based uniplate function
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The Operations
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Queries
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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]
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Get the direct children of a node. Usually using universe is more appropriate.
children = fst . uniplate |
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Transformations
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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
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Monadic variant of transform
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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.
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Monadic variant of rewrite
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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.
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Monadic variant of descend
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Others
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Return all the contexts and holes.
propUniverse x = universe x == map fst (contexts x)
propId x = all (== x) [b a | (a,b) <- contexts x]
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The one depth version of contexts
propChildren x = children x == map fst (holes x)
propId x = all (== x) [b a | (a,b) <- holes x]
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Perform a fold-like computation on each value,
technically a paramorphism
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module Data.Generics.Str |
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Produced by Haddock version 2.4.2 |