From 40022f56cfcf79d56abecf4055d9a5cc3a07447e Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom@tomsmeding.com>
Date: Tue, 21 May 2024 11:50:39 +0200
Subject: Add Ord instances on 0-dimensional arrays

This is very conservative; of course a law-abiding Ord instance can be
defined on full multi-dimensional arrays, but such an instance would be
lexicographical (anything else is even stranger), and that is
potentially unexpected and definitely does not play well with the other
numeric classes.
---
 src/Data/Array/Mixed.hs           |  3 +++
 src/Data/Array/Nested/Internal.hs | 14 ++++++++++++++
 2 files changed, 17 insertions(+)

(limited to 'src')

diff --git a/src/Data/Array/Mixed.hs b/src/Data/Array/Mixed.hs
index 320a393..baa9575 100644
--- a/src/Data/Array/Mixed.hs
+++ b/src/Data/Array/Mixed.hs
@@ -289,6 +289,9 @@ type XArray :: [Maybe Nat] -> Type -> Type
 newtype XArray sh a = XArray (S.Array (Rank sh) a)
   deriving (Show, Eq)
 
+-- | Only on scalars, because lexicographical ordering is strange on multi-dimensional arrays.
+deriving instance (Ord a, Storable a) => Ord (XArray '[] a)
+
 zeroIxX :: StaticShX sh -> IIxX sh
 zeroIxX ZKX = ZIX
 zeroIxX (_ :!% ssh) = 0 :.% zeroIxX ssh
diff --git a/src/Data/Array/Nested/Internal.hs b/src/Data/Array/Nested/Internal.hs
index b645f4a..933ce6c 100644
--- a/src/Data/Array/Nested/Internal.hs
+++ b/src/Data/Array/Nested/Internal.hs
@@ -463,6 +463,9 @@ data family Mixed sh a
 data instance Mixed sh (Primitive a) = M_Primitive !(IShX sh) !(XArray sh a)
   deriving (Show, Eq)
 
+-- | Only on scalars, because lexicographical ordering is strange on multi-dimensional arrays.
+deriving instance (Ord a, Storable a) => Ord (Mixed '[] (Primitive a))
+
 -- [PRIMITIVE ELEMENT TYPES LIST]
 newtype instance Mixed sh Int = M_Int (Mixed sh (Primitive Int)) deriving (Show, Eq)
 newtype instance Mixed sh Int64 = M_Int64 (Mixed sh (Primitive Int64)) deriving (Show, Eq)
@@ -473,6 +476,15 @@ newtype instance Mixed sh Double = M_Double (Mixed sh (Primitive Double)) derivi
 newtype instance Mixed sh () = M_Nil (Mixed sh (Primitive ())) deriving (Show, Eq)  -- no content, orthotope optimises this (via Vector)
 -- etc.
 
+-- [PRIMITIVE ELEMENT TYPES LIST]
+deriving instance Ord (Mixed '[] Int)
+deriving instance Ord (Mixed '[] Int64)
+deriving instance Ord (Mixed '[] Int32)
+deriving instance Ord (Mixed '[] CInt)
+deriving instance Ord (Mixed '[] Float)
+deriving instance Ord (Mixed '[] Double)
+deriving instance Ord (Mixed '[] ())
+
 data instance Mixed sh (a, b) = M_Tup2 !(Mixed sh a) !(Mixed sh b)
 deriving instance (Show (Mixed sh a), Show (Mixed sh b)) => Show (Mixed sh (a, b))
 -- etc.
@@ -1060,6 +1072,7 @@ type Ranked :: Nat -> Type -> Type
 newtype Ranked n a = Ranked (Mixed (Replicate n Nothing) a)
 deriving instance Show (Mixed (Replicate n Nothing) a) => Show (Ranked n a)
 deriving instance Eq (Mixed (Replicate n Nothing) a) => Eq (Ranked n a)
+deriving instance Ord (Mixed '[] a) => Ord (Ranked 0 a)
 
 -- | A shape-typed array: the full shape of the array (the sizes of its
 -- dimensions) is represented on the type level as a list of 'Nat's. Note that
@@ -1074,6 +1087,7 @@ type Shaped :: [Nat] -> Type -> Type
 newtype Shaped sh a = Shaped (Mixed (MapJust sh) a)
 deriving instance Show (Mixed (MapJust sh) a) => Show (Shaped sh a)
 deriving instance Eq (Mixed (MapJust sh) a) => Eq (Shaped sh a)
+deriving instance Ord (Mixed '[] a) => Ord (Shaped '[] a)
 
 -- just unwrap the newtype and defer to the general instance for nested arrays
 newtype instance Mixed sh (Ranked n   a) = M_Ranked (Mixed sh (Mixed (Replicate n Nothing) a))
-- 
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