{- Copyright (C) 2012 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@] Miscellaneous polymorphic operations on 'Data.Foldable.Foldable' types. -} module ToolShed.Data.Foldable( -- * Functions gather, gatherBy, -- ** Predicates hasDuplicates ) where import Control.Arrow((&&&)) import qualified Data.Foldable import qualified Data.Map {- | * Group equal (though not necessarily adjacent; c.f. 'Data.List.groupBy') elements, according to the specified comparator. * The groups are returned in ascending order, whilst their elements remain in their original order. -} gatherBy :: (Data.Foldable.Foldable f, Ord b) => (a -> b) -> f a -> [[a]] gatherBy f = Data.Map.elems . Data.Foldable.foldr (uncurry (Data.Map.insertWith (++)) . (f &&& return {-to List-monad-})) Data.Map.empty -- | A specific instance of 'gatherBy'. gather :: (Data.Foldable.Foldable f, Ord a) => f a -> [[a]] gather = gatherBy id -- | Whether the specified collection contains any equal items. hasDuplicates :: (Data.Foldable.Foldable f, Ord a) => f a -> Bool hasDuplicates = any ((> 1) . length) . gather