135 lines
3.6 KiB
Haskell
135 lines
3.6 KiB
Haskell
{-
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Helpers for the manipulation of rose trees.
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Throughout, the _trunk_ refers to successive first children in the tree.
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For example, in the tree
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> Node a [ Node b [], Node c [Node d []] ]
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the nodes in the trunk are [a,b] (note that d is not the first child of b).
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-}
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module Dodge.Layout.Tree.Polymorphic
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where
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import Dodge.RandomHelp
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import Data.Tree
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import Control.Monad.State
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import System.Random
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{- |
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Creates a linear tree.
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Safe.
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-}
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treeFromPost :: [a] -> a -> Tree a
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treeFromPost [] y = Node y []
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treeFromPost (x:xs) y = Node x [treeFromPost xs y]
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{- |
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Creates a tree with one trunk branch,
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input as a list, that ends in another tree.
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-}
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treeFromTrunk
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:: [a] -- ^ The trunk
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-> Tree a -- ^ The end of the tree
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-> Tree a
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treeFromTrunk [] t = t
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treeFromTrunk (x:xs) t = Node x [treeFromTrunk xs t]
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{- |
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Applies a function to the root of a tree.
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-}
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applyToRoot :: (a -> a) -> Tree a -> Tree a
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applyToRoot f (Node t ts) = Node (f t) ts
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-- | Consider defining this using generalised recursion patterns
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treeSize :: Tree a -> Int
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treeSize = length . flatten
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{- |
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Applies a function to a specific node determined by a list of indices.
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Unsafe (partial function).
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-}
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applyToNode :: [Int] -> (a -> a) -> Tree a -> Tree a
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applyToNode [] f t = applyToRoot f t
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applyToNode (i:is) f (Node x xs) = Node x (ys ++ [applyToNode is f z] ++ zs)
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where
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(ys, z:zs) = splitAt i xs
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{- |
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Applies a function to the first node along a trunk that satisfies a given property.
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-}
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applyToSubTrunkBy :: (a -> Bool) -> (Tree a -> Tree a) -> Tree a -> Tree a
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applyToSubTrunkBy cond f (Node x (t:ts))
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| cond x = f (Node x (t:ts))
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| otherwise = Node x (applyToSubTrunkBy cond f t : ts)
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applyToSubTrunkBy _ _ t = t
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zipTree :: Tree a -> Tree b -> Tree (a,b)
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zipTree (Node x xs) (Node y ys) = Node (x,y) $ zipWith zipTree xs ys
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{- |
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Makes each node into its child number, i.e. the index it has
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in the list of children of its parent.
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-}
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treeChildNums :: Tree a -> Tree Int
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treeChildNums = setRoot 0
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where
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setRoot :: Int -> Tree a -> Tree Int
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setRoot i (Node _ xs) = Node i (zipWith setRoot [0..] xs)
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{- |
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Makes each node into its path, i.e. the list of indices that,
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when followed from the root, lead to the node.
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-}
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treePaths :: Tree a -> Tree [a]
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treePaths (Node x xs) = (x :) <$> Node [] (map treePaths xs)
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{- |
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Picks a random path in the tree.
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Uniform probability that the path leads to any specific node.
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-}
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randomPath :: RandomGen g => Tree a -> State g [Int]
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randomPath = takeOne . flatten . treePaths . treeChildNums
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{- |
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Apply a function to the value of a node;
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the node is picked uniformly at random.
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-}
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applyToRandomNode :: RandomGen g => (a -> a) -> Tree a -> State g (Tree a)
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applyToRandomNode f t = do
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p <- randomPath t
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return $ applyToNode p f t
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{- |
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Add a forest to the end of a tree (along the trunk).
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-}
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addToTrunk :: Tree a -> [Tree a] -> Tree a
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addToTrunk (Node x []) f = Node x f
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addToTrunk (Node x (t:ts)) f = Node x (addToTrunk t f : ts)
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{- |
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Find the depth of a tree along the trunk.
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-}
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trunkDepth :: Tree a -> Int
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trunkDepth (Node _ []) = 0
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trunkDepth (Node _ (x:_)) = trunkDepth x + 1
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{- |
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Split a tree at a given point along its trunk.
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-}
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splitTrunkAt
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:: Int -- ^ Split depth
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-> Tree a -> (Tree a, [Tree a])
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splitTrunkAt 0 (Node x xs) = (Node x [],xs)
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splitTrunkAt i (Node y (x:xs)) =
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let (t, ts) = splitTrunkAt (i-1) x
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in (Node y (t : xs) , ts)
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splitTrunkAt _ (Node _ []) = error "Trying to split to short a trunk"
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{- |
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Split a tree at a random point along its trunk.
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-}
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splitTrunk :: RandomGen g => Tree a -> State g (Tree a, [Tree a])
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splitTrunk t = do
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i <- state $ randomR (0, trunkDepth t)
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return $ splitTrunkAt i t
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