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Update hylomorphism example to be more interesting

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This commit is contained in:
Rick Winfrey 2016-11-20 12:58:14 -06:00
parent e5f36bb29e
commit 2d0769d0e0
1 changed files with 8 additions and 4 deletions
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src/FDoc/RecursionSchemes.hs
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@ -107,10 +107,14 @@ hylo :: Functor f => (f b -> b) -- an algebra
Hylomorphisms work by first applying a coalgebra (anamorphism) to build up a virtual structure.
An algebra (catamorphism) is applied to this structure. Because of fusion the anamorphism and
catamorphism occur in a single pass.
catamorphism occur in a single pass rather than two separate traversals.
The example below shows how our algebra and coalgebra defined in the termToStringCata and stringToTermAna
can be utilized as a hylomorphism.
Example Usage:
stringTermHylo "indexed" => ["indexed", "leaf1", "leaf2", "leaf3"]
-}
stringTermHylo :: String -> [String]
stringTermHylo = hylo algebra coalgebra
@ -119,9 +123,9 @@ stringTermHylo = hylo algebra coalgebra
(_ :< Leaf value) -> [value]
(_ :< Indexed values) -> ["indexed"] <> (Prologue.concat values)
_ -> ["unknown"]
coalgebra representation = case representation of
"indexed" -> (Range 1 10 .: Category.MethodCall .: RNil) :< Indexed ["leaf"]
_ -> (Range 1 10 .: Category.MethodCall .: RNil) :< Leaf representation
coalgebra stringRepresentation = case stringRepresentation of
"indexed" -> (Range 1 10 .: Category.MethodCall .: RNil) :< Indexed ["leaf1", "leaf2", "leaf3"]
_ -> (Range 1 10 .: Category.MethodCall .: RNil) :< Leaf stringRepresentation
{-
Paramorphism -- primitive recursion that maintains a reference to the original subobject and its computed value.