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Update hylomorphism example to be more interesting

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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. 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 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 The example below shows how our algebra and coalgebra defined in the termToStringCata and stringToTermAna
can be utilized as a hylomorphism. can be utilized as a hylomorphism.
Example Usage:
stringTermHylo "indexed" => ["indexed", "leaf1", "leaf2", "leaf3"]
-} -}
stringTermHylo :: String -> [String] stringTermHylo :: String -> [String]
stringTermHylo = hylo algebra coalgebra stringTermHylo = hylo algebra coalgebra
@ -119,9 +123,9 @@ stringTermHylo = hylo algebra coalgebra
(_ :< Leaf value) -> [value] (_ :< Leaf value) -> [value]
(_ :< Indexed values) -> ["indexed"] <> (Prologue.concat values) (_ :< Indexed values) -> ["indexed"] <> (Prologue.concat values)
_ -> ["unknown"] _ -> ["unknown"]
coalgebra representation = case representation of coalgebra stringRepresentation = case stringRepresentation of
"indexed" -> (Range 1 10 .: Category.MethodCall .: RNil) :< Indexed ["leaf"] "indexed" -> (Range 1 10 .: Category.MethodCall .: RNil) :< Indexed ["leaf1", "leaf2", "leaf3"]
_ -> (Range 1 10 .: Category.MethodCall .: RNil) :< Leaf representation _ -> (Range 1 10 .: Category.MethodCall .: RNil) :< Leaf stringRepresentation
{- {-
Paramorphism -- primitive recursion that maintains a reference to the original subobject and its computed value. Paramorphism -- primitive recursion that maintains a reference to the original subobject and its computed value.