From 8579a03c5ae8f4812b72d477251a614d820dd1fc Mon Sep 17 00:00:00 2001
From: Mikolaj Konarski <mikolaj.konarski@funktory.com>
Date: Sun, 14 Dec 2025 23:12:30 +0100
Subject: Implement shxFromShS and shsFromShX as a newtype coerce

---
 src/Data/Array/Nested/Convert.hs | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

(limited to 'src/Data/Array/Nested/Convert.hs')

diff --git a/src/Data/Array/Nested/Convert.hs b/src/Data/Array/Nested/Convert.hs
index da1c384..3706105 100644
--- a/src/Data/Array/Nested/Convert.hs
+++ b/src/Data/Array/Nested/Convert.hs
@@ -38,6 +38,7 @@ module Data.Array.Nested.Convert (
 ) where
 
 import Control.Category
+import Data.Coerce (coerce)
 import Data.Proxy
 import Data.Type.Equality
 import GHC.TypeLits
@@ -111,7 +112,8 @@ withShsFromShR (n :$: sh) k =
       Just sn@SNat -> k (sn :$$ sh')
       Nothing -> error $ "withShsFromShR: negative dimension size (" ++ show n ++ ")"
 
--- shsFromShX re-exported
+shsFromShX :: IShX (MapJust sh) -> ShS sh
+shsFromShX = coerce
 
 -- | Produce an existential 'ShS' from an 'IShX'. If you already know that
 -- @sh'@ is @MapJust@ of something, use 'shsFromShX' instead.
@@ -126,6 +128,7 @@ withShsFromShX (SUnknown n :$% sh) k =
       Just sn@SNat -> k (sn :$$ sh')
       Nothing -> error $ "withShsFromShX: negative SUnknown dimension size (" ++ show n ++ ")"
 
+-- If it ever matters for performance, this is unsafeCoercible.
 shsFromSSX :: StaticShX (MapJust sh) -> ShS sh
 shsFromSSX = shsFromShX Prelude.. shxFromSSX
 
@@ -146,8 +149,7 @@ shxFromShR (n :$: (idx :: ShR m i)) =
     (SUnknown n :$% shxFromShR idx)
 
 shxFromShS :: ShS sh -> IShX (MapJust sh)
-shxFromShS ZSS = ZSX
-shxFromShS (n :$$ sh) = SKnown n :$% shxFromShS sh
+shxFromShS = coerce
 
 -- ixxCast re-exported
 -- shxCast re-exported
-- 
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