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Monoid instance for Exp Ordering #561

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tomsmeding merged 1 commit into from
Jan 30, 2026
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Monoid instance for Exp Ordering #561

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22 changes: 22 additions & 0 deletions src/Data/Array/Accelerate/Data/Monoid.hs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,9 @@
{-# LANGUAGE BlockArguments #-}
{-# LANGUAGE CPP #-}
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE PatternSynonyms #-}
{-# LANGUAGE ScopedTypeVariables #-}
Expand Down Expand Up @@ -46,6 +48,7 @@ import Data.Array.Accelerate.Pattern
import Data.Array.Accelerate.Smart
import Data.Array.Accelerate.Sugar.Elt
import Data.Array.Accelerate.Type
import Data.Array.Accelerate.Prelude ( match )

import Data.Function
import Data.Monoid hiding ( (<>) )
Expand Down Expand Up @@ -171,3 +174,22 @@ instance (Elt a, Elt b, Elt c, Elt d, Monoid (Exp a), Monoid (Exp b), Monoid (Ex
instance (Elt a, Elt b, Elt c, Elt d, Elt e, Monoid (Exp a), Monoid (Exp b), Monoid (Exp c), Monoid (Exp d), Monoid (Exp e)) => Monoid (Exp (a,b,c,d,e)) where
mempty = T5 mempty mempty mempty mempty mempty


-- Lexicographical ordering
-- ------------------------

-- | @since 1.4.0.0
instance Semigroup (Exp Ordering) where
x <> y = x & match \case
LT_ -> LT_
EQ_ -> y
GT_ -> GT_

stimes n x = case P.compare n 0 of
LT -> P.errorWithoutStackTrace "stimes: Exp Ordering, negative multiplier"
EQ -> EQ_
GT -> x

-- | @since 1.4.0.0
instance Monoid (Exp Ordering) where
mempty = EQ_
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