TreeAna

Example.purs

-- from: https://gist.github.com/kapranov-anton/86d44e4d382c2c38ffb5d59e331bc93a

module Main where

import Prelude

import Data.List (List)
import Data.List as List

import Control.Monad.Eff (Eff)
import Data.Foldable (fold)
import TryPureScript (DOM, h1, h2, p, text, list, indent, link, render, code)


data TreeF v a
    = Node v (List a)


treeMap :: forall a v b. (a -> b) -> TreeF v a -> TreeF v b
treeMap f (Node v xs) =
    Node v $ f <$> xs


data Tree v
    = Tree (TreeF v (Tree v))

treeAna :: forall v a. (a -> TreeF v a) -> a -> Tree v
treeAna alg =
    Tree <<< treeMap (treeAna alg) <<< alg
-- treeAna alg a =
--     Tree <<< treeMap (treeAna alg) $ alg a


treeCoalgebra :: Int -> TreeF Int Int
treeCoalgebra a =
    Node 0 List.Nil
    
    
instance showTree :: Show v => Show (Tree v)
  where show (Tree (Node v trees)) = show v <> (fold $ show <$> trees)


main :: Eff (dom :: DOM) Unit
main =
    render $ fold
      [ h1 (text $ show $ treeAna treeCoalgebra 99)
      ]