Make equal-rank-coercibility part of the interface of ListX

2 files changed, 16 insertions, 9 deletions

diff --git a/src/Data/Array/Nested/Mixed/ListX.hs b/src/Data/Array/Nested/Mixed/ListX.hs
index 51db341..e4e224b 100644
--- a/src/Data/Array/Nested/Mixed/ListX.hs
+++ b/src/Data/Array/Nested/Mixed/ListX.hs
@@ -23,7 +23,7 @@
 {-# LANGUAGE ViewPatterns #-}
 {-# OPTIONS_GHC -fplugin GHC.TypeLits.Normalise #-}
 {-# OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver #-}
-module Data.Array.Nested.Mixed.ListX (ListX, pattern ZX, pattern (::%), listxShow, lazily, lazilyConcat, lazilyForce) where
+module Data.Array.Nested.Mixed.ListX (ListX, pattern ZX, pattern (::%), listxShow, lazily, lazilyConcat, lazilyForce, Rank, coerceEqualRankListX) where
 
 import Control.DeepSeq (NFData(..))
 import Data.Foldable qualified as Foldable
@@ -38,6 +38,14 @@ import GHC.TypeLits.Orphans ()
 
 import Data.Array.Nested.Types
 
+
+-- | The length of a type-level list. If the argument is a shape, then the
+-- result is the rank of that shape.
+type family Rank sh where
+  Rank '[] = 0
+  Rank (_ : sh) = Rank sh + 1
+
+
 -- * Mixed lists implementation
 
 -- | Data invariant: each element is in WHNF (the spine may be be not forced).
@@ -132,3 +140,6 @@ instance IsList (ListX sh i) where
   fromList l = foldr seq () l `seq` ListX l
   {-# INLINE toList #-}
   toList = Foldable.toList
+
+coerceEqualRankListX :: Rank sh ~ Rank sh' => ListX sh i -> ListX sh' i
+coerceEqualRankListX (ListX l) = ListX l
diff --git a/src/Data/Array/Nested/Mixed/Shape.hs b/src/Data/Array/Nested/Mixed/Shape.hs
index 671df2c..54e19e1 100644
--- a/src/Data/Array/Nested/Mixed/Shape.hs
+++ b/src/Data/Array/Nested/Mixed/Shape.hs
@@ -24,7 +24,10 @@
 {-# LANGUAGE ViewPatterns #-}
 {-# OPTIONS_GHC -fplugin GHC.TypeLits.Normalise #-}
 {-# OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver #-}
-module Data.Array.Nested.Mixed.Shape where
+module Data.Array.Nested.Mixed.Shape (
+  module Data.Array.Nested.Mixed.Shape,
+  Rank,
+) where
 
 import Control.DeepSeq (NFData(..))
 import Control.Exception (assert)
@@ -47,13 +50,6 @@ import Data.Array.Nested.Mixed.ListX
 import Data.Array.Nested.Types
 
 
--- | The length of a type-level list. If the argument is a shape, then the
--- result is the rank of that shape.
-type family Rank sh where
-  Rank '[] = 0
-  Rank (_ : sh) = Rank sh + 1
-
-
 -- * Mixed lists
 
 {-# INLINE listxFromList #-}