{-# LANGUAGE BangPatterns               #-}
{-# LANGUAGE CPP                        #-}
{-# LANGUAGE DefaultSignatures          #-}
{-# LANGUAGE DeriveDataTypeable         #-}
{-# LANGUAGE DeriveFoldable             #-}
{-# LANGUAGE DeriveFunctor              #-}
{-# LANGUAGE DeriveGeneric              #-}
{-# LANGUAGE DeriveTraversable          #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE NoImplicitPrelude          #-}
{-# LANGUAGE Rank2Types                 #-}
{-# LANGUAGE ScopedTypeVariables        #-}
{-# LANGUAGE StandaloneDeriving         #-}

{-# OPTIONS_GHC -Wall #-}

-- this is here because of -XDefaultSignatures
{-# OPTIONS_GHC -fno-warn-missing-methods #-}

-----------------------------------------------------------------------------
-- |
-- A class for semirings (types with two binary operations, one commutative and one associative, and two respective identites), with various general-purpose instances.
--
-----------------------------------------------------------------------------

module Data.Semiring
  ( -- * Semiring typeclass
    Semiring(..)
  , (+)
  , (*)
  , (^)
  , foldMapP
  , foldMapT
  , sum
  , product
  , sum'
  , product'

    -- * Types
  , Add(..)
  , Mul(..)

    -- * Ring typeclass 
  , Ring(..)
  , (-)
  , minus 
  ) where 

import           Control.Applicative (Applicative(..), Const(..), liftA2)
import           Data.Bool (Bool(..), (||), (&&), otherwise, not)
import           Data.Complex (Complex(..))
import           Data.Eq (Eq(..))
import           Data.Fixed (Fixed, HasResolution)
import           Data.Foldable (Foldable)
import qualified Data.Foldable as Foldable
import           Data.Function ((.), const, flip, id)
import           Data.Functor (Functor(..))
#if MIN_VERSION_base(4,12,0)
import           Data.Functor.Contravariant (Predicate(..), Comparison(..), Equivalence(..), Op(..))
#endif
import           Data.Functor.Identity (Identity(..))
#if defined(VERSION_unordered_containers)
import           Data.Hashable (Hashable)
import           Data.HashMap.Strict (HashMap)
import qualified Data.HashMap.Strict as HashMap
import           Data.HashSet (HashSet)
import qualified Data.HashSet as HashSet
#endif
import           Data.Int (Int, Int8, Int16, Int32, Int64)
import           Data.Maybe (Maybe(..))
#if MIN_VERSION_base(4,12,0)
import           Data.Monoid (Ap(..))
#endif
#if defined(VERSION_containers)
--import           Data.IntMap (IntMap)
--import qualified Data.IntMap as IntMap
--import           Data.IntSet (IntSet)
--import qualified Data.IntSet as IntSet
import           Data.Map (Map)
import qualified Data.Map as Map
#endif
import           Data.Monoid (Monoid(..),Dual(..), Product(..), Sum(..))
import           Data.Ord (Ord(..), Ordering(..), compare)
#if MIN_VERSION_base(4,6,0)
import           Data.Ord (Down(..))
#endif
import           Data.Proxy (Proxy(..))
import           Data.Ratio (Ratio)
import           Data.Semigroup (Semigroup(..),Max(..), Min(..))
#if defined(VERSION_containers)
import           Data.Set (Set)
import qualified Data.Set as Set
#endif
-- #if defined(VERSION_primitive)
-- import           Data.Primitive.Array (Array(..))
-- import qualified Data.Primitive.Array as Array
-- #endif
import           Data.Traversable (Traversable)
import           Data.Typeable (Typeable)
#if defined(VERSION_vector)
import           Data.Vector (Vector)
import qualified Data.Vector as Vector
import qualified Data.Vector.Storable as SV
import qualified Data.Vector.Unboxed as UV
#endif
import           Data.Word (Word, Word8, Word16, Word32, Word64)
import           Foreign.C.Types
  (CChar, CClock, CDouble, CFloat, CInt,
   CIntMax, CIntPtr, CLLong, CLong,
   CPtrdiff, CSChar, CSUSeconds, CShort,
   CSigAtomic, CSize, CTime, CUChar, CUInt,
   CUIntMax, CUIntPtr, CULLong, CULong,
   CUSeconds, CUShort, CWchar)
import           Foreign.Ptr (IntPtr, WordPtr)
import           Foreign.Storable (Storable)
import           GHC.Base (build)
import           GHC.Enum (Enum, Bounded)
import           GHC.Float (Float, Double)
#if MIN_VERSION_base(4,6,1)
import           GHC.Generics (Generic,Generic1)
#endif
import           GHC.IO (IO)
import           GHC.Integer (Integer)
import qualified GHC.Num as Num
import           GHC.Read (Read)
import           GHC.Real (Integral, Fractional, Real, RealFrac, quot, even)
import           GHC.Show (Show)
import           Numeric.Natural (Natural)
import           System.Posix.Types
  (CCc, CDev, CGid, CIno, CMode, CNlink,
   COff, CPid, CRLim, CSpeed, CSsize,
   CTcflag, CUid, Fd)

infixl 7 *, `times`
infixl 6 +, `plus`, -, `minus`
infixr 8 ^

{--------------------------------------------------------------------
  Helpers
--------------------------------------------------------------------}

-- | Raise a number to a non-negative integral power.
-- If the power is negative, this will return 'zero'.
(^) :: (Semiring a, Integral b) => a -> b -> a
x0 ^ y0 | y0 < 0  = zero
        | y0 == 0 = one
        | otherwise = f x0 y0
  where
    f x y | even y = f (x * x) (y `quot` 2)
          | y == 1 = x
          | otherwise = g (x * x) (y `quot` 2) x
    g x y z | even y = g (x * x) (y `quot` 2) z
            | y == 1 = x * z
            | otherwise = g (x * x) (y `quot` 2) (x * z)
{-# INLINE (^) #-}

-- | Infix shorthand for 'plus'.
(+) :: Semiring a => a -> a -> a
(+) = plus
{-# INLINE (+) #-}

-- | Infix shorthand for 'times'.
(*) :: Semiring a => a -> a -> a
(*) = times
{-# INLINE (*) #-}

-- | Infix shorthand for 'minus'.
(-) :: Ring a => a -> a -> a
(-) = minus
{-# INLINE (-) #-}

-- | Map each element of the structure to a semiring, and combine the results
--   using 'plus'.
foldMapP :: (Foldable t, Semiring s) => (a -> s) -> t a -> s
foldMapP f = Foldable.foldr (plus  . f) zero
{-# INLINE foldMapP #-}

-- | Map each element of the structure to a semiring, and combine the results
--   using 'times'.
foldMapT :: (Foldable t, Semiring s) => (a -> s) -> t a -> s
foldMapT f = Foldable.foldr (times . f) one
{-# INLINE foldMapT #-}

-- | The 'sum' function computes the additive sum of the elements in a structure.
--   This function is lazy. For a strict version, see 'sum''.
sum  :: (Foldable t, Semiring a) => t a -> a
sum  = Foldable.foldr plus zero
{-# INLINE sum #-}

-- | The 'product' function computes the product of the elements in a structure.
--   This function is lazy. for a strict version, see 'product''.
product :: (Foldable t, Semiring a) => t a -> a
product = Foldable.foldr times one
{-# INLINE product #-}

-- | The 'sum'' function computes the additive sum of the elements in a structure.
--   This function is strict. For a lazy version, see 'sum'.
sum'  :: (Foldable t, Semiring a) => t a -> a
sum'  = Foldable.foldl' plus zero
{-# INLINE sum' #-}

-- | The 'product'' function computes the additive sum of the elements in a structure.
--   This function is strict. For a lazy version, see 'product'.
product' :: (Foldable t, Semiring a) => t a -> a
product' = Foldable.foldl' times one
{-# INLINE product' #-}

-- | Monoid under 'plus'. Analogous to 'Data.Monoid.Sum', but
--   uses the 'Semiring' constraint rather than 'Num'.
newtype Add a = Add { getAdd :: a }
  deriving
    ( Bounded
    , Enum
    , Eq
    , Foldable
    , Fractional
    , Functor
#if MIN_VERSION_base(4,6,1)
    , Generic
    , Generic1
#endif
    , Num.Num
    , Ord
    , Read
    , Real
    , RealFrac
    , Semiring
    , Show
    , Storable
    , Traversable
    , Typeable
    )

instance Semiring a => Semigroup (Add a) where
  (<>) = (+)
  {-# INLINE (<>) #-}

instance Semiring a => Monoid (Add a) where
  mempty = Add zero
  mappend = (<>)
  {-# INLINE mempty #-}
  {-# INLINE mappend #-}

-- | Monoid under 'times'. Analogous to 'Data.Monoid.Product', but
--   uses the 'Semiring' constraint rather than 'Num'.
newtype Mul a = Mul { getMul :: a }
  deriving
    ( Bounded
    , Enum
    , Eq
    , Foldable
    , Fractional
    , Functor
#if MIN_VERSION_base(4,6,1)
    , Generic
    , Generic1
#endif
    , Num.Num
    , Ord
    , Read
    , Real
    , RealFrac
    , Semiring
    , Show
    , Storable
    , Traversable
    , Typeable
    )

instance Semiring a => Semigroup (Mul a) where
  (<>) = (*)
  {-# INLINE (<>) #-}

instance Semiring a => Monoid (Mul a) where
  mempty = Mul one
  mappend = (<>)
  {-# INLINE mempty #-}
  {-# INLINE mappend #-}

{--------------------------------------------------------------------
  Classes
--------------------------------------------------------------------}

-- | The class of semirings (types with two binary
-- operations and two respective identities). One
-- can think of a semiring as two monoids of the same
-- underlying type: A commutative monoid and an
-- associative monoid. For any type R with a 'Prelude.Num'
-- instance, the commutative monoid is (R, '(Prelude.+)', 0)
-- and the associative monoid is (R, '(Prelude.*)', 1).
--
-- Instances should satisfy the following laws:
--
-- [/additive identity/]
-- 
--     @x '+' 'zero' = 'zero' '+' x = x@
-- 
-- [/additive associativity/]
-- 
--     @x '+' (y '+' z) = (x '+' y) '+' z@
--
-- [/additive commutativity/]
--     
--     @x '+' y = y '+' x@
--
-- [/multiplicative identity/]
-- 
--     @x '*' 'one' = 'one' '*' x = x@
--
-- [/multiplicative associativity/]
--
--     @x '*' (y '*' z) = (x '*' y) '*' z@
-- 
-- [/left- and right-distributivity of '*' over '+'/]
--
--     @x '*' (y '+' z) = (x '*' y) '+' (x '*' z)@
--     @(x '+' y) '*' z = (x '*' z) '+' (y '*' z)@
--
-- [/annihilation/]
--
--     @'zero' '*' x = x '*' 'zero' = 'zero'@

class Semiring a where
#if __GLASGOW_HASKELL__ >= 708
  {-# MINIMAL plus, zero, times, one #-}
#endif
  plus  :: a -> a -> a -- ^ Commutative Operation
  zero  :: a           -- ^ Commutative Unit
  times :: a -> a -> a -- ^ Associative Operation
  one   :: a           -- ^ Associative Unit

  -- useful for defining semirings over ground types
  default zero  :: Num.Num a => a -- ^ 0
  default one   :: Num.Num a => a -- ^ 1
  default plus  :: Num.Num a => a -> a -> a -- ^ '(Prelude.+)'
  default times :: Num.Num a => a -> a -> a -- ^ '(Prelude.*)'
  zero  = 0
  one   = 1
  plus  = (Num.+)
  times = (Num.*)

-- | The class of semirings with an additive inverse.
--
--     @'negate' a '+' a = 'zero'@

class Semiring a => Ring a where
#if __GLASGOW_HASKELL__ >= 708
  {-# MINIMAL negate #-}
#endif
  negate :: a -> a

  default negate :: Num.Num a => a -> a
  negate = Num.negate

-- | Substract two 'Ring' values. For any type 'R' with
-- a 'Prelude.Num' instance, this is the same as '(Prelude.-)'.
--
--     @x `minus` y = x '+' 'negate' y@
minus :: Ring a => a -> a -> a
minus x y = x + negate y
{-# INLINE minus #-}

{--------------------------------------------------------------------
  Instances (base)
--------------------------------------------------------------------}

instance Semiring b => Semiring (a -> b) where
  plus f g x  = f x `plus` g x
  zero        = const zero
  times f g x = f x `times` g x
  one         = const one
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

instance Ring b => Ring (a -> b) where
  negate f x = negate (f x)
  {-# INLINE negate #-}

instance Semiring () where
  plus _ _  = ()
  zero      = ()
  times _ _ = ()
  one       = ()
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

instance Ring () where
  negate _ = ()
  {-# INLINE negate #-}

instance Semiring (Proxy a) where
  plus _ _  = Proxy
  zero      = Proxy
  times _ _ = Proxy
  one       = Proxy
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

instance Semiring Bool where
  plus  = (||)
  zero  = False
  times = (&&)
  one   = True
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

instance Ring Bool where
  negate = not
  {-# INLINE negate #-}

-- See Section: List fusion
instance Semiring a => Semiring [a] where
  zero = []
  one  = [one]
  plus  = listAdd
  times = listTimes
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

instance Ring a => Ring [a] where
  negate = fmap negate
  {-# INLINE negate #-}

instance Semiring a => Semiring (Maybe a) where
  zero  = Nothing
  one   = Just one

  plus Nothing y = y
  plus x Nothing = x
  plus (Just x) (Just y) = Just (plus x y)

  times Nothing _ = Nothing
  times _ Nothing = Nothing
  times (Just x) (Just y) = Just (times x y)
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

instance Ring a => Ring (Maybe a) where
  negate = fmap negate
  {-# INLINE negate #-}

instance Semiring a => Semiring (IO a) where
  zero  = pure zero
  one   = pure one
  plus  = liftA2 plus
  times = liftA2 times
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

instance Ring a => Ring (IO a) where
  negate = fmap negate
  {-# INLINE negate #-}

instance Semiring a => Semiring (Dual a) where
  zero = Dual zero
  Dual x `plus` Dual y = Dual (y `plus` x)
  one = Dual one
  Dual x `times` Dual y = Dual (y `times` x)
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

instance Ring a => Ring (Dual a) where
  negate (Dual x) = Dual (negate x)
  {-# INLINE negate #-}

instance Semiring a => Semiring (Const a b) where
  zero = Const zero
  one  = Const one
  plus  (Const x) (Const y) = Const (x `plus`  y)
  times (Const x) (Const y) = Const (x `times` y)
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

instance Ring a => Ring (Const a b) where
  negate (Const x) = Const (negate x)
  {-# INLINE negate #-}

-- | This instance can suffer due to floating point arithmetic.
instance Ring a => Semiring (Complex a) where
  zero = zero :+ zero
  one  = one  :+ zero
  plus  (x :+ y) (x' :+ y') = plus x x' :+ plus y y'
  times (x :+ y) (x' :+ y')
    = (x * x' - (y * y')) :+ (x * y' + y * x')
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

instance Ring a => Ring (Complex a) where
  negate (x :+ y) = negate x :+ negate y
  {-# INLINE negate #-}

#if MIN_VERSION_base(4,12,0)
instance (Semiring a, Applicative f) => Semiring (Ap f a) where
  zero  = pure zero
  one   = pure one
  plus  = liftA2 plus
  times = liftA2 times
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

instance (Ring a, Applicative f) => Ring (Ap f a) where
  negate = fmap negate
  {-# INLINE negate #-}
#endif

#if MIN_VERSION_base(4,12,0)
deriving instance Semiring (Predicate a)
deriving instance Ring (Predicate a)

deriving instance Semiring a => Semiring (Equivalence a)
deriving instance Ring a => Ring (Equivalence a)

deriving instance Semiring a => Semiring (Op a b)
deriving instance Ring a => Ring (Op a b)
#endif

instance Semiring Int
instance Semiring Int8
instance Semiring Int16
instance Semiring Int32
instance Semiring Int64
instance Semiring Integer
instance Semiring Word
instance Semiring Word8
instance Semiring Word16
instance Semiring Word32
instance Semiring Word64
-- | This instance can suffer due to floating point arithmetic.
instance Semiring Float
-- | This instance can suffer due to floating point arithmetic.
instance Semiring Double
instance Semiring CUIntMax
instance Semiring CIntMax
instance Semiring CUIntPtr
instance Semiring CIntPtr
instance Semiring CSUSeconds
instance Semiring CUSeconds
instance Semiring CTime
instance Semiring CClock
instance Semiring CSigAtomic
instance Semiring CWchar
instance Semiring CSize
instance Semiring CPtrdiff
instance Semiring CDouble
instance Semiring CFloat
instance Semiring CULLong
instance Semiring CLLong
instance Semiring CULong
instance Semiring CLong
instance Semiring CUInt
instance Semiring CInt
instance Semiring CUShort
instance Semiring CShort
instance Semiring CUChar
instance Semiring CSChar
instance Semiring CChar
instance Semiring IntPtr
instance Semiring WordPtr
instance Semiring Fd
instance Semiring CRLim
instance Semiring CTcflag
instance Semiring CSpeed
instance Semiring CCc
instance Semiring CUid
instance Semiring CNlink
instance Semiring CGid
instance Semiring CSsize
instance Semiring CPid
instance Semiring COff
instance Semiring CMode
instance Semiring CIno
instance Semiring CDev
instance Semiring Natural
-- | Non-negative rational numbers form a semiring.
instance Integral a => Semiring (Ratio a)
deriving instance Semiring a => Semiring (Product a)
deriving instance Semiring a => Semiring (Sum a)
deriving instance Semiring a => Semiring (Identity a)
#if MIN_VERSION_base(4,6,0)
deriving instance Semiring a => Semiring (Down a)
#endif
deriving instance Semiring a => Semiring (Max a)
deriving instance Semiring a => Semiring (Min a)
instance HasResolution a => Semiring (Fixed a)

instance Ring Int
instance Ring Int8
instance Ring Int16
instance Ring Int32
instance Ring Int64
instance Ring Integer
instance Ring Word
instance Ring Word8
instance Ring Word16
instance Ring Word32
instance Ring Word64
instance Ring Float
instance Ring Double
instance Ring CUIntMax
instance Ring CIntMax
instance Ring CUIntPtr
instance Ring CIntPtr
instance Ring CSUSeconds
instance Ring CUSeconds
instance Ring CTime
instance Ring CClock
instance Ring CSigAtomic
instance Ring CWchar
instance Ring CSize
instance Ring CPtrdiff
instance Ring CDouble
instance Ring CFloat
instance Ring CULLong
instance Ring CLLong
instance Ring CULong
instance Ring CLong
instance Ring CUInt
instance Ring CInt
instance Ring CUShort
instance Ring CShort
instance Ring CUChar
instance Ring CSChar
instance Ring CChar
instance Ring IntPtr
instance Ring WordPtr
instance Ring Fd
instance Ring CRLim
instance Ring CTcflag
instance Ring CSpeed
instance Ring CCc
instance Ring CUid
instance Ring CNlink
instance Ring CGid
instance Ring CSsize
instance Ring CPid
instance Ring COff
instance Ring CMode
instance Ring CIno
instance Ring CDev
instance Ring Natural
instance Integral a => Ring (Ratio a)
#if MIN_VERSION_base(4,6,0)
deriving instance Ring a => Ring (Down a)
#endif
deriving instance Ring a => Ring (Product a)
deriving instance Ring a => Ring (Sum a)
deriving instance Ring a => Ring (Identity a)
deriving instance Ring a => Ring (Max a)
deriving instance Ring a => Ring (Min a)
instance HasResolution a => Ring (Fixed a)

{--------------------------------------------------------------------
  Instances (containers)
--------------------------------------------------------------------}

#if defined(VERSION_containers)

-- | The multiplication laws are satisfied for
--   any underlying 'Monoid', so we require a
--   'Monoid' contraint instead of a 'Semiring'
--   constraint since 'times' can use
--   the context of either.
instance (Ord a, Monoid a) => Semiring (Set a) where
  zero  = Set.empty
  one   = Set.singleton mempty
  plus  = Set.union
  times xs ys = Foldable.foldMap (flip Set.map ys . mappend) xs
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

-- | The multiplication laws are satisfied for
--   any underlying 'Monoid' as the key type,
--   so we require a 'Monoid' contraint instead of
--   a 'Semiring' constraint since 'times' can use
--   the context of either.
instance (Ord k, Monoid k, Semiring v) => Semiring (Map k v) where
  zero = Map.empty
  one  = Map.singleton mempty one
  plus = Map.unionWith (+)
  xs `times` ys
    = Map.fromListWith (+)
        [ (mappend k l, v * u)
        | (k,v) <- Map.toList xs
        , (l,u) <- Map.toList ys
        ]
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

--newtype IntSetP = IntSetP { intSetP :: IntSet }
--newtype IntSetT = IntSetT { intSetT :: IntSet }
--
--instance Semiring IntSetP where
--  zero = IntSetP (IntSet.empty)
--  one  = IntSetP (IntSet.singleton zero)
--  plus (IntSetP x) (IntSetP y) = IntSetP (IntSet.union x y)
--  times (IntSetP xs) (IntSetP ys) = IntSetP (foldMapIntSet (flip IntSet.map ys . plus) xs)
--
--instance Semiring IntSetT where
--  zero = IntSetT IntSet.empty
--  one  = IntSetT (IntSet.singleton one)
--  plus (IntSetT x) (IntSetT y) = IntSetT (IntSet.union x y)
--  times (IntSetT xs) (IntSetT ys) = IntSetT (foldMapIntSet (flip IntSet.map ys . times) xs)
--
--foldMapIntSet :: Monoid m => (Int -> m) -> IntSet -> m
--foldMapIntSet f = IntSet.foldl' (flip (mappend . f)) mempty
--{-# INLINE foldMapIntSet #-}

--instance (Semiring a) => Semiring (IntMap a) where
--  zero = IntMap.empty
--  one  = IntMap.singleton zero one
--  plus = IntMap.unionWith (+)
--  xs `times` ys
--    = IntMap.fromListWith (+)
--        [ (plus k l, v * u)
--        | (k,v) <- IntMap.toList xs
--        , (l,u) <- IntMap.toList ys
--        ]
#endif

{--------------------------------------------------------------------
  Instances (unordered-containers)
--------------------------------------------------------------------}

#if defined(VERSION_unordered_containers)

-- | The multiplication laws are satisfied for
--   any underlying 'Monoid', so we require a
--   'Monoid' contraint instead of a 'Semiring'
--   constraint since 'times' can use
--   the context of either.
instance (Eq a, Hashable a, Monoid a) => Semiring (HashSet a) where
  zero = HashSet.empty
  one  = HashSet.singleton mempty
  plus = HashSet.union
  times xs ys = Foldable.foldMap (flip HashSet.map ys . mappend) xs
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

-- | The multiplication laws are satisfied for
--   any underlying 'Monoid' as the key type,
--   so we require a 'Monoid' contraint instead of
--   a 'Semiring' constraint since 'times' can use
--   the context of either.
instance (Eq k, Hashable k, Monoid k, Semiring v) => Semiring (HashMap k v) where
  zero = HashMap.empty
  one  = HashMap.singleton mempty one
  plus = HashMap.unionWith (+)
  xs `times` ys
    = HashMap.fromListWith (+)
        [ (mappend k l, v * u)
        | (k,v) <- HashMap.toList xs
        , (l,u) <- HashMap.toList ys
        ]
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}
#endif

{--------------------------------------------------------------------
  Instances (primitive)
--------------------------------------------------------------------}

#if defined(VERSION_primitive)
-- | The multiplication laws are satisfied for
--   any underlying 'Monoid', so we require a
--   'Monoid' contraint instead of a 'Semiring'
--   constraint since 'times' can use
--   the context of either.
-- instance (Monoid a) => Semiring (Array a) where
--   zero  = mempty
--   one   = runST e where
--     e :: forall s. Monoid a => ST s (Array a)
--     e = (Array.newArray 1 mempty) >>= Array.unsafeFreezeArray
--   plus _ _ = mempty
--   times _ _ = mempty
--   {-# INLINE plus  #-}
--   {-# INLINE zero  #-}
--   {-# INLINE times #-}
--   {-# INLINE one   #-}
#endif

{--------------------------------------------------------------------
  Instances (vector)
--------------------------------------------------------------------}

#if defined(VERSION_vector)
instance Semiring a => Semiring (Vector a) where
  zero  = Vector.empty
  one   = Vector.singleton one
  plus xs ys =
    case compare (Vector.length xs) (Vector.length ys) of
      EQ -> Vector.zipWith (+) xs ys
      LT -> Vector.unsafeAccumulate (+) ys (Vector.indexed xs)
      GT -> Vector.unsafeAccumulate (+) xs (Vector.indexed ys)
  times signal kernel
    | Vector.null signal = Vector.empty
    | Vector.null kernel = Vector.empty
    | otherwise = Vector.generate (slen + klen - 1) f
    where
      !slen = Vector.length signal
      !klen = Vector.length kernel
      f n = Foldable.foldl'
        (\a k -> a +
                 Vector.unsafeIndex signal k *
                 Vector.unsafeIndex kernel (n - k)
        )
        zero
        [kmin .. kmax]
        where
          !kmin = max 0 (n - (klen - 1))
          !kmax = min n (slen - 1)
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}

instance Ring a => Ring (Vector a) where
  negate = Vector.map negate
  {-# INLINE negate #-}

instance (UV.Unbox a, Semiring a) => Semiring (UV.Vector a) where
  zero = UV.empty
  one  = UV.singleton one
  plus xs ys =
    case compare (UV.length xs) (UV.length ys) of
      EQ -> UV.zipWith (+) xs ys
      LT -> UV.unsafeAccumulate (+) ys (UV.indexed xs)
      GT -> UV.unsafeAccumulate (+) xs (UV.indexed ys)
  times signal kernel
    | UV.null signal = UV.empty
    | UV.null kernel = UV.empty
    | otherwise = UV.generate (slen + klen - 1) f
    where
      !slen = UV.length signal
      !klen = UV.length kernel
      f n = Foldable.foldl'
        (\a k -> a +
                 UV.unsafeIndex signal k *
                 UV.unsafeIndex kernel (n - k)
        )
        zero
        [kmin .. kmax]
        where
          !kmin = max 0 (n - (klen - 1))
          !kmax = min n (slen - 1)
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}
 
instance (UV.Unbox a, Ring a) => Ring (UV.Vector a) where
  negate = UV.map negate
  {-# INLINE negate #-}

instance (SV.Storable a, Semiring a) => Semiring (SV.Vector a) where
  zero = SV.empty
  one = SV.singleton one
  plus xs ys =
    case compare lxs lys of
      EQ -> SV.zipWith (+) xs ys
      LT -> SV.unsafeAccumulate_ (+) ys (SV.enumFromN 0 lxs) xs
      GT -> SV.unsafeAccumulate_ (+) xs (SV.enumFromN 0 lys) ys
    where
      lxs = SV.length xs
      lys = SV.length ys
  times signal kernel
    | SV.null signal = SV.empty
    | SV.null kernel = SV.empty
    | otherwise = SV.generate (slen + klen - 1) f
      where
        !slen = SV.length signal
        !klen = SV.length kernel
        f n = Foldable.foldl'
          (\a k -> a +
                  SV.unsafeIndex signal k *
                  SV.unsafeIndex kernel (n - k))
                zero
                [kmin .. kmax]
          where
            !kmin = max 0 (n - (klen - 1))
            !kmax = min n (slen - 1)
  {-# INLINE plus  #-}
  {-# INLINE zero  #-}
  {-# INLINE times #-}
  {-# INLINE one   #-}
  
instance (SV.Storable a, Ring a) => Ring (SV.Vector a) where
  negate = SV.map negate
  {-# INLINE negate #-}
#endif

-- [Section: List fusion]
-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
listAdd, listTimes :: Semiring a => [a] -> [a] -> [a]
listAdd [] ys = ys
listAdd xs [] = xs
listAdd (x:xs) (y:ys) = (x + y) : listAdd xs ys
{-# NOINLINE [0] listAdd #-}

listTimes [] (_:xs) = zero : listTimes [] xs
listTimes (_:xs) [] = zero : listTimes xs []
listTimes [] [] = []
listTimes (x:xs) (y:ys) = (x * y) : listTimes xs ys
{-# NOINLINE [0] listTimes #-}

type ListBuilder a = forall b. (a -> b -> b) -> b -> b

{-# RULES 
"listAddFB/left"  forall    (g :: ListBuilder a). listAdd    (build g) = listAddFBL g
"listAddFB/right" forall xs (g :: ListBuilder a). listAdd xs (build g) = listAddFBR xs g
  #-}

-- a definition of listAdd which can be fused on its left argument
listAddFBL :: Semiring a => ListBuilder a -> [a] -> [a]
listAddFBL xf = xf f id where
  f x xs (y:ys) = x + y : xs ys
  f x xs []     = x : xs []

-- a definition of listAdd which can be fused on its right argument
listAddFBR :: Semiring a => [a] -> ListBuilder a -> [a]
listAddFBR xs' yf = yf f id xs' where
  f y ys (x:xs) = x + y : ys xs
  f y ys []     = y : ys []