{- Copyright (C) 2010-2015 Dr. Alistair Ward This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>. -} {- | [@AUTHOR@] Dr. Alistair Ward [@DESCRIPTION@] * Defines a specific type of tree-structure, which is composed from either a datum, or a list of Tree-lists; <https://en.wikipedia.org/wiki/Rose_Tree>. * This more general tree-structure has the shape of a regular-expression match. * This contrasts with the typical binary-tree, which is either empty, or contains a (left Tree, datum, right Tree). -} module RegExDot.Tree( -- * Types -- ** Type-synonyms -- TreeList, -- ** Data-types Tree(..), -- * Functions pop ) where import qualified Control.Arrow import qualified Control.DeepSeq import qualified Data.Foldable import qualified Data.List import qualified Data.Monoid -- | A general purpose tree-type structure. data Tree a = Leaf a -- ^ The payload. | Node [TreeList a] -- ^ Recurse. N.B.: a list of lists is required to contain the /MatchLists/ resulting from repeated /Alternatives/. deriving Eq -- | A list of 'Tree's; significant only because it is the essence of the recursive nature of 'Tree'. type TreeList a = [Tree a] instance Show a => Show (Tree a) where showsPrec _ (Leaf a) = shows a showsPrec _ (Node treeLists) = showList treeLists instance Read a => Read (Tree a) where readsPrec _ node@('[' : _) = Control.Arrow.first Node `map` readList node {-singleton-} readsPrec _ leaf = Control.Arrow.first Leaf `map` reads leaf {-singleton-} instance Control.DeepSeq.NFData a => Control.DeepSeq.NFData (Tree a) where rnf (Leaf a) = Control.DeepSeq.rnf a rnf (Node l) = Control.DeepSeq.rnf l instance Functor Tree where fmap f (Leaf a) = Leaf $ f a fmap f (Node treeLists) = Node $ map (fmap {-recurse-} f `map`) treeLists instance Data.Foldable.Foldable Tree where foldMap f (Leaf a) = f a -- CAVEAT: 'f' should be Associative, as required by a Monoid. foldMap f (Node treeLists) = Data.List.foldl' (Data.List.foldl' (\monoid -> (monoid `Data.Monoid.mappend`) . Data.Foldable.foldMap f)) Data.Monoid.mempty treeLists -- | Deconstruct the specified 'Node'; i.e. lop the apex from the 'Tree', leaving a flat top. pop :: Tree a -- ^ The tree from which to extract the list of trees hanging immediately beneath its apex. -> [TreeList a] pop (Node treeLists) = treeLists pop _ = error "RegExDot.Tree.pop:\tunexpected Leaf"