~alcinnz/haskell-stylist

ref: b93db8b7308658745714cf326e1ba7348fca0f5e haskell-stylist/src/Data/CSS/StyleTree.hs -rw-r--r-- 1.3 KiB
b93db8b7 — Adrian Cochrane Implement whitespace collapse, togglable via white-space: pre/normal; 4 years ago 
                                                                                
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-- | Abstracts away tree traversals.
-- Mostly used by callers including (soon) XML Conduit Stylist,
-- but also used internally for generating counter text.
module Data.CSS.StyleTree(StyleTree(..), treeOrder, treeOrder', Path, treeMap) where

data StyleTree p = StyleTree {
    style :: p,
    children :: [StyleTree p]
}

type Path = [Integer]
treeOrder :: (c -> c -> Path -> p -> (c, p')) ->
    c -> StyleTree p -> StyleTree p'
treeOrder cb ctxt tree = StyleTree
    (snd $ cb ctxt ctxt [] $ style tree)
    (snd $ treeOrder' cb ctxt ctxt [0] $ children tree)
treeOrder' :: (c -> c -> Path -> p -> (c, p')) ->
    c -> c -> Path -> [StyleTree p] -> (c, [StyleTree p'])
treeOrder' cb prevContext context (num:path) (node:nodes) = (tailContext, StyleTree node' children' : nodes')
    where
        (selfContext, node') = cb prevContext context (num:path) $ style node
        (childContext, children') = treeOrder' cb selfContext selfContext (0:num:path) $ children node
        (tailContext, nodes') = treeOrder' cb selfContext childContext (num + 1:path) nodes
treeOrder' _ _ context _ [] = (context, [])
treeOrder' _ _ _ [] _ = error "Invalid path during tree traversal!"

treeMap :: (p -> p') -> StyleTree p -> StyleTree p'
treeMap cb = treeOrder (\_ _ _ p -> ((), cb p)) ()