{- Copyright (C) 2018 Dr. Alistair Ward This file is part of BishBosh. BishBosh 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. BishBosh 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 BishBosh. If not, see <http://www.gnu.org/licenses/>. -} {- | [@AUTHOR@] Dr. Alistair Ward [@DESCRIPTION@] * An interface for data which can support the concept of being empty. * N.B.: the empty state of the type must be unique. * cf. "Data.Default" or 'zero' for a numeric type. -} module BishBosh.Property.Empty( -- * Type-classes Empty(..) ) where -- | An interface which data which can support the concept of being empty, may implement. class Empty a where empty :: a -- ^ Constant. instance (Empty a, Empty b) => Empty (a, b) where empty = (empty, empty)