{- | An effect modelling nondeterminism with choice and failure. Nondeterministic operations are encapsulated by the 'Alternative' class, where 'empty' represents failure and '<|>' represents choice. This module re-exports the 'Alternative' interface. If you can't or don't want to use 'Alternative', you can use the 'Control.Effect.Empty.empty' and 'Control.Effect.Choose.<|>' operations (from "Control.Effect.Empty" and "Control.Effect.Choose" respectively) directly, as the 'NonDet' effect is the composition of 'Choose' and 'Empty'. Predefined carriers: * "Control.Carrier.NonDet.Church", which collects all branches' results using an @Alternative@ functor. * If 'NonDet' is the last effect in a stack, it can be interpreted directly into a @[]@. @since 0.1.0.0 -} module Control.Effect.NonDet ( -- * NonDet effects NonDet , module Control.Effect.Choose , module Control.Effect.Empty , oneOf , foldMapA -- * Re-exports , Alternative(..) , Algebra , Effect , Has , MonadPlus(..) , guard , optional , run ) where import Control.Algebra import Control.Applicative (Alternative(..), optional) import Control.Effect.Choose (Choose(..)) import Control.Effect.Empty (Empty(..)) import Control.Effect.NonDet.Internal (NonDet) import Control.Monad (MonadPlus(..), guard) import Data.Coerce import Data.Monoid (Alt(..)) -- | Nondeterministically choose an element from a 'Foldable' collection. -- This can be used to emulate the style of nondeterminism associated with -- programming in the list monad: -- -- @ -- pythagoreanTriples = do -- a <- oneOf [1..10] -- b <- oneOf [1..10] -- c <- oneOf [1..10] -- guard (a^2 + b^2 == c^2) -- pure (a, b, c) -- @ -- -- @since 1.0.0.0 oneOf :: (Foldable t, Alternative m) => t a -> m a oneOf = foldMapA pure -- | Map a 'Foldable' collection of values into a nondeterministic computation using the supplied action. -- -- @since 1.0.0.0 foldMapA :: (Foldable t, Alternative m) => (a -> m b) -> t a -> m b foldMapA f = getAlt #. foldMap (Alt #. f) -- | Compose a function operationally equivalent to 'id' on the left. -- -- cf https://github.com/fused-effects/diffused-effects/pull/1#discussion_r323560758 (#.) :: Coercible b c => (b -> c) -> (a -> b) -> (a -> c) (#.) _ = coerce {-# INLINE (#.) #-}