From a65306ba5d80891b20ac86fa3a3242f9497751e6 Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom@tomsmeding.com>
Date: Thu, 30 May 2024 11:58:40 +0200
Subject: Refactor Mixed (modules, regular function names)

---
 src/Data/Array/Mixed/Internal/Arith.hs          | 435 ++++++++++++++++++++++
 src/Data/Array/Mixed/Internal/Arith/Foreign.hs  |  55 +++
 src/Data/Array/Mixed/Internal/Arith/Lists.hs    |  78 ++++
 src/Data/Array/Mixed/Internal/Arith/Lists/TH.hs |  82 +++++
 src/Data/Array/Mixed/Lemmas.hs                  |  47 +++
 src/Data/Array/Mixed/Permutation.hs             | 252 +++++++++++++
 src/Data/Array/Mixed/Shape.hs                   | 455 ++++++++++++++++++++++++
 src/Data/Array/Mixed/Types.hs                   | 110 ++++++
 8 files changed, 1514 insertions(+)
 create mode 100644 src/Data/Array/Mixed/Internal/Arith.hs
 create mode 100644 src/Data/Array/Mixed/Internal/Arith/Foreign.hs
 create mode 100644 src/Data/Array/Mixed/Internal/Arith/Lists.hs
 create mode 100644 src/Data/Array/Mixed/Internal/Arith/Lists/TH.hs
 create mode 100644 src/Data/Array/Mixed/Lemmas.hs
 create mode 100644 src/Data/Array/Mixed/Permutation.hs
 create mode 100644 src/Data/Array/Mixed/Shape.hs
 create mode 100644 src/Data/Array/Mixed/Types.hs

(limited to 'src/Data/Array/Mixed')

diff --git a/src/Data/Array/Mixed/Internal/Arith.hs b/src/Data/Array/Mixed/Internal/Arith.hs
new file mode 100644
index 0000000..cf6820b
--- /dev/null
+++ b/src/Data/Array/Mixed/Internal/Arith.hs
@@ -0,0 +1,435 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE ViewPatterns #-}
+{-# OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver #-}
+module Data.Array.Mixed.Internal.Arith where
+
+import Control.Monad (forM, guard)
+import qualified Data.Array.Internal as OI
+import qualified Data.Array.Internal.RankedG as RG
+import qualified Data.Array.Internal.RankedS as RS
+import Data.Bits
+import Data.Int
+import Data.List (sort)
+import qualified Data.Vector.Storable as VS
+import qualified Data.Vector.Storable.Mutable as VSM
+import Foreign.C.Types
+import Foreign.Ptr
+import Foreign.Storable (Storable)
+import GHC.TypeLits
+import Language.Haskell.TH
+import System.IO.Unsafe
+
+import Data.Array.Mixed.Internal.Arith.Foreign
+import Data.Array.Mixed.Internal.Arith.Lists
+
+
+liftVEltwise1 :: Storable a
+              => SNat n
+              -> (VS.Vector a -> VS.Vector a)
+              -> RS.Array n a -> RS.Array n a
+liftVEltwise1 SNat f arr@(RS.A (RG.A sh (OI.T strides offset vec)))
+  | Just prefixSz <- stridesDense sh strides =
+      let vec' = f (VS.slice offset prefixSz vec)
+      in RS.A (RG.A sh (OI.T strides 0 vec'))
+  | otherwise = RS.fromVector sh (f (RS.toVector arr))
+
+liftVEltwise2 :: Storable a
+              => SNat n
+              -> (Either a (VS.Vector a) -> Either a (VS.Vector a) -> VS.Vector a)
+              -> RS.Array n a -> RS.Array n a -> RS.Array n a
+liftVEltwise2 SNat f
+    arr1@(RS.A (RG.A sh1 (OI.T strides1 offset1 vec1)))
+    arr2@(RS.A (RG.A sh2 (OI.T strides2 offset2 vec2)))
+  | sh1 /= sh2 = error $ "liftVEltwise2: shapes unequal: " ++ show sh1 ++ " vs " ++ show sh2
+  | product sh1 == 0 = arr1  -- if the arrays are empty, just return one of the empty inputs
+  | otherwise = case (stridesDense sh1 strides1, stridesDense sh2 strides2) of
+      (Just 1, Just 1) ->  -- both are a (potentially replicated) scalar; just apply f to the scalars
+        let vec' = f (Left (vec1 VS.! offset1)) (Left (vec2 VS.! offset2))
+        in RS.A (RG.A sh1 (OI.T strides1 0 vec'))
+      (Just 1, Just n) ->  -- scalar * dense
+        RS.fromVector sh1 (f (Left (vec1 VS.! offset1)) (Right (VS.slice offset2 n vec2)))
+      (Just n, Just 1) ->  -- dense * scalar
+        RS.fromVector sh1 (f (Right (VS.slice offset1 n vec1)) (Left (vec2 VS.! offset2)))
+      (_, _) ->  -- fallback case
+        RS.fromVector sh1 (f (Right (RS.toVector arr1)) (Right (RS.toVector arr2)))
+
+-- | Given the shape vector and the stride vector, return whether this vector
+-- of strides uses a dense prefix of its backing array. If so, the number of
+-- elements in this prefix is returned.
+-- This excludes any offset.
+stridesDense :: [Int] -> [Int] -> Maybe Int
+stridesDense sh _ | any (<= 0) sh = Just 0
+stridesDense sh str =
+  -- sort dimensions on their stride, ascending, dropping any zero strides
+  case dropWhile ((== 0) . fst) (sort (zip str sh)) of
+    [] -> Just 1
+    (1, n) : (unzip -> (str', sh')) -> checkCover n sh' str'
+    _ -> Nothing  -- if the smallest stride is not 1, it will never be dense
+  where
+    -- Given size of currently densely covered region at beginning of the
+    -- array, the remaining shape vector and the corresponding remaining stride
+    -- vector, return whether this all together covers a dense prefix of the
+    -- array. If it does, return the number of elements in this prefix.
+    checkCover :: Int -> [Int] -> [Int] -> Maybe Int
+    checkCover block [] [] = Just block
+    checkCover block (n : sh') (s : str') = guard (s <= block) >> checkCover (max block (n * s)) sh' str'
+    checkCover _ _ _ = error "Orthotope array's shape vector and stride vector have different lengths"
+
+{-# NOINLINE vectorOp1 #-}
+vectorOp1 :: forall a b. Storable a
+          => (Ptr a -> Ptr b)
+          -> (Int64 -> Ptr b -> Ptr b -> IO ())
+          -> VS.Vector a -> VS.Vector a
+vectorOp1 ptrconv f v = unsafePerformIO $ do
+  outv <- VSM.unsafeNew (VS.length v)
+  VSM.unsafeWith outv $ \poutv ->
+    VS.unsafeWith v $ \pv ->
+      f (fromIntegral (VS.length v)) (ptrconv poutv) (ptrconv pv)
+  VS.unsafeFreeze outv
+
+-- | If two vectors are given, assumes that they have the same length.
+{-# NOINLINE vectorOp2 #-}
+vectorOp2 :: forall a b. Storable a
+          => (a -> b)
+          -> (Ptr a -> Ptr b)
+          -> (a -> a -> a)
+          -> (Int64 -> Ptr b -> b -> Ptr b -> IO ())  -- sv
+          -> (Int64 -> Ptr b -> Ptr b -> b -> IO ())  -- vs
+          -> (Int64 -> Ptr b -> Ptr b -> Ptr b -> IO ())  -- vv
+          -> Either a (VS.Vector a) -> Either a (VS.Vector a) -> VS.Vector a
+vectorOp2 valconv ptrconv fss fsv fvs fvv = \cases
+  (Left x) (Left y) -> VS.singleton (fss x y)
+
+  (Left x) (Right vy) ->
+    unsafePerformIO $ do
+      outv <- VSM.unsafeNew (VS.length vy)
+      VSM.unsafeWith outv $ \poutv ->
+        VS.unsafeWith vy $ \pvy ->
+          fsv (fromIntegral (VS.length vy)) (ptrconv poutv) (valconv x) (ptrconv pvy)
+      VS.unsafeFreeze outv
+
+  (Right vx) (Left y) ->
+    unsafePerformIO $ do
+      outv <- VSM.unsafeNew (VS.length vx)
+      VSM.unsafeWith outv $ \poutv ->
+        VS.unsafeWith vx $ \pvx ->
+          fvs (fromIntegral (VS.length vx)) (ptrconv poutv) (ptrconv pvx) (valconv y)
+      VS.unsafeFreeze outv
+
+  (Right vx) (Right vy)
+    | VS.length vx == VS.length vy ->
+        unsafePerformIO $ do
+          outv <- VSM.unsafeNew (VS.length vx)
+          VSM.unsafeWith outv $ \poutv ->
+            VS.unsafeWith vx $ \pvx ->
+              VS.unsafeWith vy $ \pvy ->
+                fvv (fromIntegral (VS.length vx)) (ptrconv poutv) (ptrconv pvx) (ptrconv pvy)
+          VS.unsafeFreeze outv
+    | otherwise -> error $ "vectorOp: unequal lengths: " ++ show (VS.length vx) ++ " /= " ++ show (VS.length vy)
+
+-- TODO: test all the weird cases of this function
+-- | Reduce along the inner dimension
+{-# NOINLINE vectorRedInnerOp #-}
+vectorRedInnerOp :: forall a b n. (Num a, Storable a)
+                 => SNat n
+                 -> (a -> b)
+                 -> (Ptr a -> Ptr b)
+                 -> (Int64 -> Ptr b -> b -> Ptr b -> IO ())  -- ^ scale by constant
+                 -> (Int64 -> Ptr Int64 -> Ptr Int64 -> Ptr b -> Ptr b -> IO ())  -- ^ reduction kernel
+                 -> RS.Array (n + 1) a -> RS.Array n a
+vectorRedInnerOp sn@SNat valconv ptrconv fscale fred (RS.A (RG.A sh (OI.T strides offset vec)))
+  | null sh = error "unreachable"
+  | last sh <= 0 = RS.stretch (init sh) (RS.fromList (map (const 1) (init sh)) [0])
+  | any (<= 0) (init sh) = RS.A (RG.A (init sh) (OI.T (map (const 0) (init strides)) 0 VS.empty))
+  -- now the input array is nonempty
+  | last sh == 1 = RS.A (RG.A (init sh) (OI.T (init strides) offset vec))
+  | last strides == 0 =
+      liftVEltwise1 sn
+        (vectorOp1 id (\n pout px -> fscale n (ptrconv pout) (valconv (fromIntegral (last sh))) (ptrconv px)))
+        (RS.A (RG.A (init sh) (OI.T (init strides) offset vec)))
+  -- now there is useful work along the inner dimension
+  | otherwise =
+      let -- filter out zero-stride dimensions; the reduction kernel need not concern itself with those
+          (shF, stridesF) = unzip $ filter ((/= 0) . snd) (zip sh strides)
+          ndimsF = length shF
+      in unsafePerformIO $ do
+           outv <- VSM.unsafeNew (product (init shF))
+           VSM.unsafeWith outv $ \poutv ->
+             VS.unsafeWith (VS.fromListN ndimsF (map fromIntegral shF)) $ \pshF ->
+               VS.unsafeWith (VS.fromListN ndimsF (map fromIntegral stridesF)) $ \pstridesF ->
+                 VS.unsafeWith (VS.slice offset (VS.length vec - offset) vec) $ \pvec ->
+                   fred (fromIntegral ndimsF) pshF pstridesF (ptrconv poutv) (ptrconv pvec)
+           RS.fromVector (init sh) <$> VS.unsafeFreeze outv
+
+flipOp :: (Int64 -> Ptr a -> a -> Ptr a -> IO ())
+       ->  Int64 -> Ptr a -> Ptr a -> a -> IO ()
+flipOp f n out v s = f n out s v
+
+$(fmap concat . forM typesList $ \arithtype -> do
+    let ttyp = conT (atType arithtype)
+    fmap concat . forM [minBound..maxBound] $ \arithop -> do
+      let name = mkName (aboName arithop ++ "Vector" ++ nameBase (atType arithtype))
+          cnamebase = "c_binary_" ++ atCName arithtype
+          c_ss = varE (aboNumOp arithop)
+          c_sv = varE (mkName (cnamebase ++ "_sv")) `appE` litE (integerL (fromIntegral (aboEnum arithop)))
+          c_vs = varE (mkName (cnamebase ++ "_vs")) `appE` litE (integerL (fromIntegral (aboEnum arithop)))
+          c_vv = varE (mkName (cnamebase ++ "_vv")) `appE` litE (integerL (fromIntegral (aboEnum arithop)))
+      sequence [SigD name <$>
+                     [t| forall n. SNat n -> RS.Array n $ttyp -> RS.Array n $ttyp -> RS.Array n $ttyp |]
+               ,do body <- [| \sn -> liftVEltwise2 sn (vectorOp2 id id $c_ss $c_sv $c_vs $c_vv) |]
+                   return $ FunD name [Clause [] (NormalB body) []]])
+
+$(fmap concat . forM floatTypesList $ \arithtype -> do
+    let ttyp = conT (atType arithtype)
+    fmap concat . forM [minBound..maxBound] $ \arithop -> do
+      let name = mkName (afboName arithop ++ "Vector" ++ nameBase (atType arithtype))
+          cnamebase = "c_fbinary_" ++ atCName arithtype
+          c_ss = varE (afboNumOp arithop)
+          c_sv = varE (mkName (cnamebase ++ "_sv")) `appE` litE (integerL (fromIntegral (afboEnum arithop)))
+          c_vs = varE (mkName (cnamebase ++ "_vs")) `appE` litE (integerL (fromIntegral (afboEnum arithop)))
+          c_vv = varE (mkName (cnamebase ++ "_vv")) `appE` litE (integerL (fromIntegral (afboEnum arithop)))
+      sequence [SigD name <$>
+                     [t| forall n. SNat n -> RS.Array n $ttyp -> RS.Array n $ttyp -> RS.Array n $ttyp |]
+               ,do body <- [| \sn -> liftVEltwise2 sn (vectorOp2 id id $c_ss $c_sv $c_vs $c_vv) |]
+                   return $ FunD name [Clause [] (NormalB body) []]])
+
+$(fmap concat . forM typesList $ \arithtype -> do
+    let ttyp = conT (atType arithtype)
+    fmap concat . forM [minBound..maxBound] $ \arithop -> do
+      let name = mkName (auoName arithop ++ "Vector" ++ nameBase (atType arithtype))
+          c_op = varE (mkName ("c_unary_" ++ atCName arithtype)) `appE` litE (integerL (fromIntegral (auoEnum arithop)))
+      sequence [SigD name <$>
+                     [t| forall n. SNat n -> RS.Array n $ttyp -> RS.Array n $ttyp |]
+               ,do body <- [| \sn -> liftVEltwise1 sn (vectorOp1 id $c_op) |]
+                   return $ FunD name [Clause [] (NormalB body) []]])
+
+$(fmap concat . forM floatTypesList $ \arithtype -> do
+    let ttyp = conT (atType arithtype)
+    fmap concat . forM [minBound..maxBound] $ \arithop -> do
+      let name = mkName (afuoName arithop ++ "Vector" ++ nameBase (atType arithtype))
+          c_op = varE (mkName ("c_funary_" ++ atCName arithtype)) `appE` litE (integerL (fromIntegral (afuoEnum arithop)))
+      sequence [SigD name <$>
+                     [t| forall n. SNat n -> RS.Array n $ttyp -> RS.Array n $ttyp |]
+               ,do body <- [| \sn -> liftVEltwise1 sn (vectorOp1 id $c_op) |]
+                   return $ FunD name [Clause [] (NormalB body) []]])
+
+$(fmap concat . forM typesList $ \arithtype -> do
+    let ttyp = conT (atType arithtype)
+    fmap concat . forM [minBound..maxBound] $ \arithop -> do
+      let name = mkName (aroName arithop ++ "Vector" ++ nameBase (atType arithtype))
+          c_op = varE (mkName ("c_reduce_" ++ atCName arithtype)) `appE` litE (integerL (fromIntegral (aroEnum arithop)))
+          c_scale_op = varE (mkName ("c_binary_" ++ atCName arithtype ++ "_sv")) `appE` litE (integerL (fromIntegral (aboEnum BO_MUL)))
+      sequence [SigD name <$>
+                     [t| forall n. SNat n -> RS.Array (n + 1) $ttyp -> RS.Array n $ttyp |]
+               ,do body <- [| \sn -> vectorRedInnerOp sn id id $c_scale_op $c_op |]
+                   return $ FunD name [Clause [] (NormalB body) []]])
+
+-- This branch is ostensibly a runtime branch, but will (hopefully) be
+-- constant-folded away by GHC.
+intWidBranch1 :: forall i n. (FiniteBits i, Storable i)
+              => (Int64 -> Ptr Int32 -> Ptr Int32 -> IO ())
+              -> (Int64 -> Ptr Int64 -> Ptr Int64 -> IO ())
+              -> (SNat n -> RS.Array n i -> RS.Array n i)
+intWidBranch1 f32 f64 sn
+  | finiteBitSize (undefined :: i) == 32 = liftVEltwise1 sn (vectorOp1 @i @Int32 castPtr f32)
+  | finiteBitSize (undefined :: i) == 64 = liftVEltwise1 sn (vectorOp1 @i @Int64 castPtr f64)
+  | otherwise = error "Unsupported Int width"
+
+intWidBranch2 :: forall i n. (FiniteBits i, Storable i, Integral i)
+              => (i -> i -> i)  -- ss
+                 -- int32
+              -> (Int64 -> Ptr Int32 -> Int32 -> Ptr Int32 -> IO ())  -- sv
+              -> (Int64 -> Ptr Int32 -> Ptr Int32 -> Int32 -> IO ())  -- vs
+              -> (Int64 -> Ptr Int32 -> Ptr Int32 -> Ptr Int32 -> IO ())  -- vv
+                 -- int64
+              -> (Int64 -> Ptr Int64 -> Int64 -> Ptr Int64 -> IO ())  -- sv
+              -> (Int64 -> Ptr Int64 -> Ptr Int64 -> Int64 -> IO ())  -- vs
+              -> (Int64 -> Ptr Int64 -> Ptr Int64 -> Ptr Int64 -> IO ())  -- vv
+              -> (SNat n -> RS.Array n i -> RS.Array n i -> RS.Array n i)
+intWidBranch2 ss sv32 vs32 vv32 sv64 vs64 vv64 sn
+  | finiteBitSize (undefined :: i) == 32 = liftVEltwise2 sn (vectorOp2 @i @Int32 fromIntegral castPtr ss sv32 vs32 vv32)
+  | finiteBitSize (undefined :: i) == 64 = liftVEltwise2 sn (vectorOp2 @i @Int64 fromIntegral castPtr ss sv64 vs64 vv64)
+  | otherwise = error "Unsupported Int width"
+
+intWidBranchRed :: forall i n. (FiniteBits i, Storable i, Integral i)
+                => -- int32
+                   (Int64 -> Ptr Int32 -> Int32 -> Ptr Int32 -> IO ())  -- ^ scale by constant
+                -> (Int64 -> Ptr Int64 -> Ptr Int64 -> Ptr Int32 -> Ptr Int32 -> IO ())  -- ^ reduction kernel
+                   -- int64
+                -> (Int64 -> Ptr Int64 -> Int64 -> Ptr Int64 -> IO ())  -- ^ scale by constant
+                -> (Int64 -> Ptr Int64 -> Ptr Int64 -> Ptr Int64 -> Ptr Int64 -> IO ())  -- ^ reduction kernel
+                -> (SNat n -> RS.Array (n + 1) i -> RS.Array n i)
+intWidBranchRed fsc32 fred32 fsc64 fred64 sn
+  | finiteBitSize (undefined :: i) == 32 = vectorRedInnerOp @i @Int32 sn fromIntegral castPtr fsc32 fred32
+  | finiteBitSize (undefined :: i) == 64 = vectorRedInnerOp @i @Int64 sn fromIntegral castPtr fsc64 fred64
+  | otherwise = error "Unsupported Int width"
+
+class NumElt a where
+  numEltAdd :: SNat n -> RS.Array n a -> RS.Array n a -> RS.Array n a
+  numEltSub :: SNat n -> RS.Array n a -> RS.Array n a -> RS.Array n a
+  numEltMul :: SNat n -> RS.Array n a -> RS.Array n a -> RS.Array n a
+  numEltNeg :: SNat n -> RS.Array n a -> RS.Array n a
+  numEltAbs :: SNat n -> RS.Array n a -> RS.Array n a
+  numEltSignum :: SNat n -> RS.Array n a -> RS.Array n a
+  numEltSum1Inner :: SNat n -> RS.Array (n + 1) a -> RS.Array n a
+  numEltProduct1Inner :: SNat n -> RS.Array (n + 1) a -> RS.Array n a
+
+instance NumElt Int32 where
+  numEltAdd = addVectorInt32
+  numEltSub = subVectorInt32
+  numEltMul = mulVectorInt32
+  numEltNeg = negVectorInt32
+  numEltAbs = absVectorInt32
+  numEltSignum = signumVectorInt32
+  numEltSum1Inner = sum1VectorInt32
+  numEltProduct1Inner = product1VectorInt32
+
+instance NumElt Int64 where
+  numEltAdd = addVectorInt64
+  numEltSub = subVectorInt64
+  numEltMul = mulVectorInt64
+  numEltNeg = negVectorInt64
+  numEltAbs = absVectorInt64
+  numEltSignum = signumVectorInt64
+  numEltSum1Inner = sum1VectorInt64
+  numEltProduct1Inner = product1VectorInt64
+
+instance NumElt Float where
+  numEltAdd = addVectorFloat
+  numEltSub = subVectorFloat
+  numEltMul = mulVectorFloat
+  numEltNeg = negVectorFloat
+  numEltAbs = absVectorFloat
+  numEltSignum = signumVectorFloat
+  numEltSum1Inner = sum1VectorFloat
+  numEltProduct1Inner = product1VectorFloat
+
+instance NumElt Double where
+  numEltAdd = addVectorDouble
+  numEltSub = subVectorDouble
+  numEltMul = mulVectorDouble
+  numEltNeg = negVectorDouble
+  numEltAbs = absVectorDouble
+  numEltSignum = signumVectorDouble
+  numEltSum1Inner = sum1VectorDouble
+  numEltProduct1Inner = product1VectorDouble
+
+instance NumElt Int where
+  numEltAdd = intWidBranch2 @Int (+)
+                (c_binary_i32_sv (aboEnum BO_ADD)) (flipOp (c_binary_i32_sv (aboEnum BO_ADD))) (c_binary_i32_vv (aboEnum BO_ADD))
+                (c_binary_i64_sv (aboEnum BO_ADD)) (flipOp (c_binary_i64_sv (aboEnum BO_ADD))) (c_binary_i64_vv (aboEnum BO_ADD))
+  numEltSub = intWidBranch2 @Int (-)
+                (c_binary_i32_sv (aboEnum BO_SUB)) (flipOp (c_binary_i32_sv (aboEnum BO_SUB))) (c_binary_i32_vv (aboEnum BO_SUB))
+                (c_binary_i64_sv (aboEnum BO_SUB)) (flipOp (c_binary_i64_sv (aboEnum BO_SUB))) (c_binary_i64_vv (aboEnum BO_SUB))
+  numEltMul = intWidBranch2 @Int (*)
+                (c_binary_i32_sv (aboEnum BO_MUL)) (flipOp (c_binary_i32_sv (aboEnum BO_MUL))) (c_binary_i32_vv (aboEnum BO_MUL))
+                (c_binary_i64_sv (aboEnum BO_MUL)) (flipOp (c_binary_i64_sv (aboEnum BO_MUL))) (c_binary_i64_vv (aboEnum BO_MUL))
+  numEltNeg = intWidBranch1 @Int (c_unary_i32 (auoEnum UO_NEG)) (c_unary_i64 (auoEnum UO_NEG))
+  numEltAbs = intWidBranch1 @Int (c_unary_i32 (auoEnum UO_ABS)) (c_unary_i64 (auoEnum UO_ABS))
+  numEltSignum = intWidBranch1 @Int (c_unary_i32 (auoEnum UO_SIGNUM)) (c_unary_i64 (auoEnum UO_SIGNUM))
+  numEltSum1Inner = intWidBranchRed @Int
+                      (c_binary_i32_sv (aboEnum BO_MUL)) (c_reduce_i32 (aroEnum RO_SUM1))
+                      (c_binary_i64_sv (aboEnum BO_MUL)) (c_reduce_i64 (aroEnum RO_SUM1))
+  numEltProduct1Inner = intWidBranchRed @Int
+                          (c_binary_i32_sv (aboEnum BO_MUL)) (c_reduce_i32 (aroEnum RO_PRODUCT1))
+                          (c_binary_i64_sv (aboEnum BO_MUL)) (c_reduce_i64 (aroEnum RO_PRODUCT1))
+
+instance NumElt CInt where
+  numEltAdd = intWidBranch2 @CInt (+)
+                (c_binary_i32_sv (aboEnum BO_ADD)) (flipOp (c_binary_i32_sv (aboEnum BO_ADD))) (c_binary_i32_vv (aboEnum BO_ADD))
+                (c_binary_i64_sv (aboEnum BO_ADD)) (flipOp (c_binary_i64_sv (aboEnum BO_ADD))) (c_binary_i64_vv (aboEnum BO_ADD))
+  numEltSub = intWidBranch2 @CInt (-)
+                (c_binary_i32_sv (aboEnum BO_SUB)) (flipOp (c_binary_i32_sv (aboEnum BO_SUB))) (c_binary_i32_vv (aboEnum BO_SUB))
+                (c_binary_i64_sv (aboEnum BO_SUB)) (flipOp (c_binary_i64_sv (aboEnum BO_SUB))) (c_binary_i64_vv (aboEnum BO_SUB))
+  numEltMul = intWidBranch2 @CInt (*)
+                (c_binary_i32_sv (aboEnum BO_MUL)) (flipOp (c_binary_i32_sv (aboEnum BO_MUL))) (c_binary_i32_vv (aboEnum BO_MUL))
+                (c_binary_i64_sv (aboEnum BO_MUL)) (flipOp (c_binary_i64_sv (aboEnum BO_MUL))) (c_binary_i64_vv (aboEnum BO_MUL))
+  numEltNeg = intWidBranch1 @CInt (c_unary_i32 (auoEnum UO_NEG)) (c_unary_i64 (auoEnum UO_NEG))
+  numEltAbs = intWidBranch1 @CInt (c_unary_i32 (auoEnum UO_ABS)) (c_unary_i64 (auoEnum UO_ABS))
+  numEltSignum = intWidBranch1 @CInt (c_unary_i32 (auoEnum UO_SIGNUM)) (c_unary_i64 (auoEnum UO_SIGNUM))
+  numEltSum1Inner = intWidBranchRed @CInt
+                      (c_binary_i32_sv (aboEnum BO_MUL)) (c_reduce_i32 (aroEnum RO_SUM1))
+                      (c_binary_i64_sv (aboEnum BO_MUL)) (c_reduce_i64 (aroEnum RO_SUM1))
+  numEltProduct1Inner = intWidBranchRed @CInt
+                          (c_binary_i32_sv (aboEnum BO_MUL)) (c_reduce_i32 (aroEnum RO_PRODUCT1))
+                          (c_binary_i64_sv (aboEnum BO_MUL)) (c_reduce_i64 (aroEnum RO_PRODUCT1))
+
+class FloatElt a where
+  floatEltDiv :: SNat n -> RS.Array n a -> RS.Array n a -> RS.Array n a
+  floatEltPow :: SNat n -> RS.Array n a -> RS.Array n a -> RS.Array n a
+  floatEltLogbase :: SNat n -> RS.Array n a -> RS.Array n a -> RS.Array n a
+  floatEltRecip :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltExp :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltLog :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltSqrt :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltSin :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltCos :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltTan :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltAsin :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltAcos :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltAtan :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltSinh :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltCosh :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltTanh :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltAsinh :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltAcosh :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltAtanh :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltLog1p :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltExpm1 :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltLog1pexp :: SNat n -> RS.Array n a -> RS.Array n a
+  floatEltLog1mexp :: SNat n -> RS.Array n a -> RS.Array n a
+
+instance FloatElt Float where
+  floatEltDiv = divVectorFloat
+  floatEltPow = powVectorFloat
+  floatEltLogbase = logbaseVectorFloat
+  floatEltRecip = recipVectorFloat
+  floatEltExp = expVectorFloat
+  floatEltLog = logVectorFloat
+  floatEltSqrt = sqrtVectorFloat
+  floatEltSin = sinVectorFloat
+  floatEltCos = cosVectorFloat
+  floatEltTan = tanVectorFloat
+  floatEltAsin = asinVectorFloat
+  floatEltAcos = acosVectorFloat
+  floatEltAtan = atanVectorFloat
+  floatEltSinh = sinhVectorFloat
+  floatEltCosh = coshVectorFloat
+  floatEltTanh = tanhVectorFloat
+  floatEltAsinh = asinhVectorFloat
+  floatEltAcosh = acoshVectorFloat
+  floatEltAtanh = atanhVectorFloat
+  floatEltLog1p = log1pVectorFloat
+  floatEltExpm1 = expm1VectorFloat
+  floatEltLog1pexp = log1pexpVectorFloat
+  floatEltLog1mexp = log1mexpVectorFloat
+
+instance FloatElt Double where
+  floatEltDiv = divVectorDouble
+  floatEltPow = powVectorDouble
+  floatEltLogbase = logbaseVectorDouble
+  floatEltRecip = recipVectorDouble
+  floatEltExp = expVectorDouble
+  floatEltLog = logVectorDouble
+  floatEltSqrt = sqrtVectorDouble
+  floatEltSin = sinVectorDouble
+  floatEltCos = cosVectorDouble
+  floatEltTan = tanVectorDouble
+  floatEltAsin = asinVectorDouble
+  floatEltAcos = acosVectorDouble
+  floatEltAtan = atanVectorDouble
+  floatEltSinh = sinhVectorDouble
+  floatEltCosh = coshVectorDouble
+  floatEltTanh = tanhVectorDouble
+  floatEltAsinh = asinhVectorDouble
+  floatEltAcosh = acoshVectorDouble
+  floatEltAtanh = atanhVectorDouble
+  floatEltLog1p = log1pVectorDouble
+  floatEltExpm1 = expm1VectorDouble
+  floatEltLog1pexp = log1pexpVectorDouble
+  floatEltLog1mexp = log1mexpVectorDouble
diff --git a/src/Data/Array/Mixed/Internal/Arith/Foreign.hs b/src/Data/Array/Mixed/Internal/Arith/Foreign.hs
new file mode 100644
index 0000000..6fc7229
--- /dev/null
+++ b/src/Data/Array/Mixed/Internal/Arith/Foreign.hs
@@ -0,0 +1,55 @@
+{-# LANGUAGE ForeignFunctionInterface #-}
+{-# LANGUAGE TemplateHaskell #-}
+module Data.Array.Mixed.Internal.Arith.Foreign where
+
+import Control.Monad
+import Data.Int
+import Data.Maybe
+import Foreign.C.Types
+import Foreign.Ptr
+import Language.Haskell.TH
+
+import Data.Array.Mixed.Internal.Arith.Lists
+
+
+$(fmap concat . forM typesList $ \arithtype -> do
+    let ttyp = conT (atType arithtype)
+    let base = "binary_" ++ atCName arithtype
+    sequence $ catMaybes
+      [Just (ForeignD . ImportF CCall Unsafe ("oxarop_" ++ base ++ "_sv") (mkName ("c_" ++ base ++ "_sv")) <$>
+               [t| CInt -> Int64 -> Ptr $ttyp -> $ttyp -> Ptr $ttyp -> IO () |])
+      ,Just (ForeignD . ImportF CCall Unsafe ("oxarop_" ++ base ++ "_vv") (mkName ("c_" ++ base ++ "_vv")) <$>
+               [t| CInt -> Int64 -> Ptr $ttyp -> Ptr $ttyp -> Ptr $ttyp -> IO () |])
+      ,Just (ForeignD . ImportF CCall Unsafe ("oxarop_" ++ base ++ "_vs") (mkName ("c_" ++ base ++ "_vs")) <$>
+               [t| CInt -> Int64 -> Ptr $ttyp -> Ptr $ttyp -> $ttyp -> IO () |])
+      ])
+
+$(fmap concat . forM floatTypesList $ \arithtype -> do
+    let ttyp = conT (atType arithtype)
+    let base = "fbinary_" ++ atCName arithtype
+    sequence $ catMaybes
+      [Just (ForeignD . ImportF CCall Unsafe ("oxarop_" ++ base ++ "_sv") (mkName ("c_" ++ base ++ "_sv")) <$>
+               [t| CInt -> Int64 -> Ptr $ttyp -> $ttyp -> Ptr $ttyp -> IO () |])
+      ,Just (ForeignD . ImportF CCall Unsafe ("oxarop_" ++ base ++ "_vv") (mkName ("c_" ++ base ++ "_vv")) <$>
+               [t| CInt -> Int64 -> Ptr $ttyp -> Ptr $ttyp -> Ptr $ttyp -> IO () |])
+      ,Just (ForeignD . ImportF CCall Unsafe ("oxarop_" ++ base ++ "_vs") (mkName ("c_" ++ base ++ "_vs")) <$>
+               [t| CInt -> Int64 -> Ptr $ttyp -> Ptr $ttyp -> $ttyp -> IO () |])
+      ])
+
+$(fmap concat . forM typesList $ \arithtype -> do
+    let ttyp = conT (atType arithtype)
+    let base = "unary_" ++ atCName arithtype
+    pure . ForeignD . ImportF CCall Unsafe ("oxarop_" ++ base) (mkName ("c_" ++ base)) <$>
+      [t| CInt -> Int64 -> Ptr $ttyp -> Ptr $ttyp -> IO () |])
+
+$(fmap concat . forM floatTypesList $ \arithtype -> do
+    let ttyp = conT (atType arithtype)
+    let base = "funary_" ++ atCName arithtype
+    pure . ForeignD . ImportF CCall Unsafe ("oxarop_" ++ base) (mkName ("c_" ++ base)) <$>
+      [t| CInt -> Int64 -> Ptr $ttyp -> Ptr $ttyp -> IO () |])
+
+$(fmap concat . forM typesList $ \arithtype -> do
+    let ttyp = conT (atType arithtype)
+    let base = "reduce_" ++ atCName arithtype
+    pure . ForeignD . ImportF CCall Unsafe ("oxarop_" ++ base) (mkName ("c_" ++ base)) <$>
+      [t| CInt -> Int64 -> Ptr Int64 -> Ptr Int64 -> Ptr $ttyp -> Ptr $ttyp -> IO () |])
diff --git a/src/Data/Array/Mixed/Internal/Arith/Lists.hs b/src/Data/Array/Mixed/Internal/Arith/Lists.hs
new file mode 100644
index 0000000..a284bc1
--- /dev/null
+++ b/src/Data/Array/Mixed/Internal/Arith/Lists.hs
@@ -0,0 +1,78 @@
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE TemplateHaskell #-}
+module Data.Array.Mixed.Internal.Arith.Lists where
+
+import Data.Char
+import Data.Int
+import Language.Haskell.TH
+
+import Data.Array.Mixed.Internal.Arith.Lists.TH
+
+
+data ArithType = ArithType
+  { atType :: Name  -- ''Int32
+  , atCName :: String  -- "i32"
+  }
+
+floatTypesList :: [ArithType]
+floatTypesList =
+  [ArithType ''Float "float"
+  ,ArithType ''Double "double"
+  ]
+
+typesList :: [ArithType]
+typesList =
+  [ArithType ''Int32 "i32"
+  ,ArithType ''Int64 "i64"
+  ]
+  ++ floatTypesList
+
+-- data ArithBOp = BO_ADD | BO_SUB | BO_MUL deriving (Show, Enum, Bounded)
+$(genArithDataType Binop "ArithBOp")
+
+$(genArithNameFun Binop ''ArithBOp "aboName" (map toLower . drop 3))
+$(genArithEnumFun Binop ''ArithBOp "aboEnum")
+
+$(do clauses <- readArithLists Binop
+                  (\name _num hsop -> return (Clause [ConP (mkName name) [] []]
+                                                     (NormalB (VarE 'mkName `AppE` LitE (StringL hsop)))
+                                                     []))
+                  return
+     sequence [SigD (mkName "aboNumOp") <$> [t| ArithBOp -> Name |]
+              ,return $ FunD (mkName "aboNumOp") clauses])
+
+
+-- data ArithFBOp = FB_DIV deriving (Show, Enum, Bounded)
+$(genArithDataType FBinop "ArithFBOp")
+
+$(genArithNameFun FBinop ''ArithFBOp "afboName" (map toLower . drop 3))
+$(genArithEnumFun FBinop ''ArithFBOp "afboEnum")
+
+$(do clauses <- readArithLists FBinop
+                  (\name _num hsop -> return (Clause [ConP (mkName name) [] []]
+                                                     (NormalB (VarE 'mkName `AppE` LitE (StringL hsop)))
+                                                     []))
+                  return
+     sequence [SigD (mkName "afboNumOp") <$> [t| ArithFBOp -> Name |]
+              ,return $ FunD (mkName "afboNumOp") clauses])
+
+
+-- data ArithUOp = UO_NEG | UO_ABS | UO_SIGNUM | ... deriving (Show, Enum, Bounded)
+$(genArithDataType Unop "ArithUOp")
+
+$(genArithNameFun Unop ''ArithUOp "auoName" (map toLower . drop 3))
+$(genArithEnumFun Unop ''ArithUOp "auoEnum")
+
+
+-- data ArithFUOp = FU_RECIP | ... deriving (Show, Enum, Bounded)
+$(genArithDataType FUnop "ArithFUOp")
+
+$(genArithNameFun FUnop ''ArithFUOp "afuoName" (map toLower . drop 3))
+$(genArithEnumFun FUnop ''ArithFUOp "afuoEnum")
+
+
+-- data ArithRedOp = RO_SUM1 | RO_PRODUCT1 deriving (Show, Enum, Bounded)
+$(genArithDataType Redop "ArithRedOp")
+
+$(genArithNameFun Redop ''ArithRedOp "aroName" (map toLower . drop 3))
+$(genArithEnumFun Redop ''ArithRedOp "aroEnum")
diff --git a/src/Data/Array/Mixed/Internal/Arith/Lists/TH.hs b/src/Data/Array/Mixed/Internal/Arith/Lists/TH.hs
new file mode 100644
index 0000000..8b7d05f
--- /dev/null
+++ b/src/Data/Array/Mixed/Internal/Arith/Lists/TH.hs
@@ -0,0 +1,82 @@
+{-# LANGUAGE TemplateHaskellQuotes #-}
+module Data.Array.Mixed.Internal.Arith.Lists.TH where
+
+import Control.Monad
+import Control.Monad.IO.Class
+import Data.Maybe
+import Foreign.C.Types
+import Language.Haskell.TH
+import Language.Haskell.TH.Syntax
+import Text.Read
+
+
+data OpKind = Binop | FBinop | Unop | FUnop | Redop
+  deriving (Show, Eq)
+
+readArithLists :: OpKind
+               -> (String -> Int -> String -> Q a)
+               -> ([a] -> Q r)
+               -> Q r
+readArithLists targetkind fop fcombine = do
+  addDependentFile "cbits/arith_lists.h"
+  lns <- liftIO $ lines <$> readFile "cbits/arith_lists.h"
+
+  mvals <- forM lns $ \line -> do
+    if null (dropWhile (== ' ') line)
+      then return Nothing
+      else do let (kind, name, num, aux) = parseLine line
+              if kind == targetkind
+                then Just <$> fop name num aux
+                else return Nothing
+
+  fcombine (catMaybes mvals)
+  where
+    parseLine s0
+      | ("LIST_", s1) <- splitAt 5 s0
+      , (kindstr, '(' : s2) <- break (== '(') s1
+      , (f1, ',' : s3) <- parseField s2
+      , (f2, ',' : s4) <- parseField s3
+      , (f3, ')' : _) <- parseField s4
+      , Just kind <- parseKind kindstr
+      , let name = f1
+      , Just num <- readMaybe f2
+      , let aux = f3
+      = (kind, name, num, aux)
+      | otherwise
+      = error $ "readArithLists: unrecognised line in cbits/arith_lists.h: " ++ show s0
+
+    parseField s = break (`elem` ",)") (dropWhile (== ' ') s)
+
+    parseKind "BINOP" = Just Binop
+    parseKind "FBINOP" = Just FBinop
+    parseKind "UNOP" = Just Unop
+    parseKind "FUNOP" = Just FUnop
+    parseKind "REDOP" = Just Redop
+    parseKind _ = Nothing
+
+genArithDataType :: OpKind -> String -> Q [Dec]
+genArithDataType kind dtname = do
+  cons <- readArithLists kind
+            (\name _num _ -> return $ NormalC (mkName name) [])
+            return
+  return [DataD [] (mkName dtname) [] Nothing cons [DerivClause Nothing [ConT ''Show, ConT ''Enum, ConT ''Bounded]]]
+
+genArithNameFun :: OpKind -> Name -> String -> (String -> String) -> Q [Dec]
+genArithNameFun kind dtname funname nametrans = do
+  clauses <- readArithLists kind
+               (\name _num _ -> return (Clause [ConP (mkName name) [] []]
+                                               (NormalB (LitE (StringL (nametrans name))))
+                                               []))
+               return
+  return [SigD (mkName funname) (ArrowT `AppT` ConT dtname `AppT` ConT ''String)
+         ,FunD (mkName funname) clauses]
+
+genArithEnumFun :: OpKind -> Name -> String -> Q [Dec]
+genArithEnumFun kind dtname funname = do
+  clauses <- readArithLists kind
+               (\name num _ -> return (Clause [ConP (mkName name) [] []]
+                                              (NormalB (LitE (IntegerL (fromIntegral num))))
+                                              []))
+               return
+  return [SigD (mkName funname) (ArrowT `AppT` ConT dtname `AppT` ConT ''CInt)
+         ,FunD (mkName funname) clauses]
diff --git a/src/Data/Array/Mixed/Lemmas.hs b/src/Data/Array/Mixed/Lemmas.hs
new file mode 100644
index 0000000..30ec9c0
--- /dev/null
+++ b/src/Data/Array/Mixed/Lemmas.hs
@@ -0,0 +1,47 @@
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeOperators #-}
+{-# OPTIONS_GHC -fplugin GHC.TypeLits.Normalise #-}
+{-# OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE DataKinds #-}
+module Data.Array.Mixed.Lemmas where
+
+import Data.Proxy
+import Data.Type.Equality
+import GHC.TypeLits
+
+import Data.Array.Mixed.Shape
+import Data.Array.Mixed.Types
+
+
+lemRankApp :: forall sh1 sh2.
+              StaticShX sh1 -> StaticShX sh2
+           -> Rank (sh1 ++ sh2) :~: Rank sh1 + Rank sh2
+lemRankApp ZKX _ = Refl
+lemRankApp (_ :!% (ssh1 :: StaticShX sh1T)) ssh2
+  = lem2 (Proxy @(Rank sh1T)) Proxy Proxy $
+      lem (Proxy @(Rank sh2)) (Proxy @(Rank sh1T)) (Proxy @(Rank (sh1T ++ sh2))) $
+        lemRankApp ssh1 ssh2
+  where
+    lem :: proxy a -> proxy b -> proxy c
+        -> c :~: b + a
+        -> b + a :~: c
+    lem _ _ _ Refl = Refl
+
+    lem2 :: proxy a -> proxy b -> proxy c
+         -> (a + b :~: c)
+         -> c + 1 :~: (a + 1 + b)
+    lem2 _ _ _ Refl = Refl
+
+lemRankAppComm :: StaticShX sh1 -> StaticShX sh2
+               -> Rank (sh1 ++ sh2) :~: Rank (sh2 ++ sh1)
+lemRankAppComm _ _ = unsafeCoerceRefl  -- TODO improve this
+
+lemKnownNatRank :: IShX sh -> Dict KnownNat (Rank sh)
+lemKnownNatRank ZSX = Dict
+lemKnownNatRank (_ :$% sh) | Dict <- lemKnownNatRank sh = Dict
+
+lemKnownNatRankSSX :: StaticShX sh -> Dict KnownNat (Rank sh)
+lemKnownNatRankSSX ZKX = Dict
+lemKnownNatRankSSX (_ :!% ssh) | Dict <- lemKnownNatRankSSX ssh = Dict
diff --git a/src/Data/Array/Mixed/Permutation.hs b/src/Data/Array/Mixed/Permutation.hs
new file mode 100644
index 0000000..2710018
--- /dev/null
+++ b/src/Data/Array/Mixed/Permutation.hs
@@ -0,0 +1,252 @@
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE QuantifiedConstraints #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE UndecidableInstances #-}
+{-# OPTIONS_GHC -fplugin GHC.TypeLits.Normalise #-}
+{-# OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver #-}
+module Data.Array.Mixed.Permutation where
+
+import Data.Coerce (coerce)
+import Data.Functor.Const
+import Data.List (sort)
+import Data.Proxy
+import Data.Type.Bool
+import Data.Type.Equality
+import Data.Type.Ord
+import GHC.TypeError
+import GHC.TypeLits
+import qualified GHC.TypeNats as TN
+
+import Data.Array.Mixed.Shape
+import Data.Array.Mixed.Types
+
+
+-- * Permutations
+
+-- | A "backward" permutation of a dimension list. The operation on the
+-- dimension list is most similar to 'Data.Vector.backpermute'; see 'Permute'
+-- for code that implements this.
+data Perm list where
+  PNil :: Perm '[]
+  PCons :: SNat a -> Perm l -> Perm (a : l)
+infixr 5 `PCons`
+deriving instance Show (Perm list)
+deriving instance Eq (Perm list)
+
+permLengthSNat :: Perm list -> SNat (Rank list)
+permLengthSNat PNil = SNat
+permLengthSNat (_ `PCons` l) | SNat <- permLengthSNat l = SNat
+
+permFromList :: [Int] -> (forall list. Perm list -> r) -> r
+permFromList [] k = k PNil
+permFromList (x : xs) k = withSomeSNat (fromIntegral x) $ \case
+  Just sn -> permFromList xs $ \list -> k (sn `PCons` list)
+  Nothing -> error $ "Data.Array.Mixed.permFromList: negative number in list: " ++ show x
+
+permToList :: Perm list -> [Natural]
+permToList PNil = mempty
+permToList (x `PCons` l) = TN.fromSNat x : permToList l
+
+permToList' :: Perm list -> [Int]
+permToList' = map fromIntegral . permToList
+
+
+-- ** Applying permutations
+
+type family Elem x l where
+  Elem x '[] = 'False
+  Elem x (x : _) = 'True
+  Elem x (_ : ys) = Elem x ys
+
+type family AllElem' as bs where
+  AllElem' '[] bs = 'True
+  AllElem' (a : as) bs = Elem a bs && AllElem' as bs
+
+type AllElem as bs = Assert (AllElem' as bs)
+  (TypeError (Text "The elements of " :<>: ShowType as :<>: Text " are not all in " :<>: ShowType bs))
+
+type family Count i n where
+  Count n n = '[]
+  Count i n = i : Count (i + 1) n
+
+type IsPermutation as = (AllElem as (Count 0 (Rank as)), AllElem (Count 0 (Rank as)) as)
+
+type family Index i sh where
+  Index 0 (n : sh) = n
+  Index i (_ : sh) = Index (i - 1) sh
+
+type family Permute is sh where
+  Permute '[] sh = '[]
+  Permute (i : is) sh = Index i sh : Permute is sh
+
+type PermutePrefix is sh = Permute is (TakeLen is sh) ++ DropLen is sh
+
+type family TakeLen ref l where
+  TakeLen '[] l = '[]
+  TakeLen (_ : ref) (x : xs) = x : TakeLen ref xs
+
+type family DropLen ref l where
+  DropLen '[] l = l
+  DropLen (_ : ref) (_ : xs) = DropLen ref xs
+
+listxTakeLen :: forall f is sh. Perm is -> ListX sh f -> ListX (TakeLen is sh) f
+listxTakeLen PNil _ = ZX
+listxTakeLen (_ `PCons` is) (n ::% sh) = n ::% listxTakeLen is sh
+listxTakeLen (_ `PCons` _) ZX = error "IsPermutation longer than shape"
+
+listxDropLen :: forall f is sh. Perm is -> ListX sh f -> ListX (DropLen is sh) f
+listxDropLen PNil sh = sh
+listxDropLen (_ `PCons` is) (_ ::% sh) = listxDropLen is sh
+listxDropLen (_ `PCons` _) ZX = error "IsPermutation longer than shape"
+
+listxPermute :: forall f is sh. Perm is -> ListX sh f -> ListX (Permute is sh) f
+listxPermute PNil _ = ZX
+listxPermute (i `PCons` (is :: Perm is')) (sh :: ListX sh f) =
+  listxIndex (Proxy @is') (Proxy @sh) i sh (listxPermute is sh)
+
+listxIndex :: forall f is shT i sh. Proxy is -> Proxy shT -> SNat i -> ListX sh f -> ListX (Permute is shT) f -> ListX (Index i sh : Permute is shT) f
+listxIndex _ _ SZ (n ::% _) rest = n ::% rest
+listxIndex p pT (SS (i :: SNat i')) ((_ :: f n) ::% (sh :: ListX sh' f)) rest
+  | Refl <- lemIndexSucc (Proxy @i') (Proxy @n) (Proxy @sh')
+  = listxIndex p pT i sh rest
+listxIndex _ _ _ ZX _ = error "Index into empty shape"
+
+listxPermutePrefix :: forall f is sh. Perm is -> ListX sh f -> ListX (PermutePrefix is sh) f
+listxPermutePrefix perm sh = listxAppend (listxPermute perm (listxTakeLen perm sh)) (listxDropLen perm sh)
+
+ixxPermutePrefix :: forall i is sh. Perm is -> IxX sh i -> IxX (PermutePrefix is sh) i
+ixxPermutePrefix = coerce (listxPermutePrefix @(Const i))
+
+ssxTakeLen :: forall is sh. Perm is -> StaticShX sh -> StaticShX (TakeLen is sh)
+ssxTakeLen = coerce (listxTakeLen @(SMayNat () SNat))
+
+ssxDropLen :: Perm is -> StaticShX sh -> StaticShX (DropLen is sh)
+ssxDropLen = coerce (listxDropLen @(SMayNat () SNat))
+
+ssxPermute :: Perm is -> StaticShX sh -> StaticShX (Permute is sh)
+ssxPermute = coerce (listxPermute @(SMayNat () SNat))
+
+ssxIndex :: Proxy is -> Proxy shT -> SNat i -> StaticShX sh -> StaticShX (Permute is shT) -> StaticShX (Index i sh : Permute is shT)
+ssxIndex p1 p2 = coerce (listxIndex @(SMayNat () SNat) p1 p2)
+
+ssxPermutePrefix :: Perm is -> StaticShX sh -> StaticShX (PermutePrefix is sh)
+ssxPermutePrefix = coerce (listxPermutePrefix @(SMayNat () SNat))
+
+shxPermutePrefix :: Perm is -> IShX sh -> IShX (PermutePrefix is sh)
+shxPermutePrefix = coerce (listxPermutePrefix @(SMayNat Int SNat))
+
+
+-- * Operations on permutations
+
+-- TODO: test this thing more properly
+permInverse :: Perm is
+            -> (forall is'.
+                     IsPermutation is'
+                  => Perm is'
+                  -> (forall sh. Rank sh ~ Rank is => StaticShX sh -> Permute is' (Permute is sh) :~: sh)
+                  -> r)
+            -> r
+permInverse = \perm k ->
+  genPerm perm $ \(invperm :: Perm is') ->
+    let sn = permLengthSNat invperm
+    in case (provePerm1 (Proxy @is') sn invperm, provePerm2 (SNat @0) sn invperm) of
+         (Just Refl, Just Refl) ->
+           k invperm
+             (\ssh -> case provePermInverse perm invperm ssh of
+                        Just eq -> eq
+                        Nothing -> error $ "permInverse: did not generate inverse? perm = " ++ show perm
+                                           ++ " ; invperm = " ++ show invperm)
+         _ -> error $ "permInverse: did not generate permutation? perm = " ++ show perm
+                      ++ " ; invperm = " ++ show invperm
+  where
+    genPerm :: Perm is -> (forall is'. Perm is' -> r) -> r
+    genPerm perm =
+      let permList = permToList' perm
+      in toHList $ map snd (sort (zip permList [0..]))
+      where
+        toHList :: [Natural] -> (forall is'. Perm is' -> r) -> r
+        toHList [] k = k PNil
+        toHList (n : ns) k = toHList ns $ \l -> TN.withSomeSNat n $ \sn -> k (PCons sn l)
+
+    lemElemCount :: (0 <= n, Compare n m ~ LT) => proxy n -> proxy m -> Elem n (Count 0 m) :~: True
+    lemElemCount _ _ = unsafeCoerceRefl
+
+    lemCount :: (OrdCond (Compare i n) True False True ~ True) => proxy i -> proxy n -> Count i n :~: i : Count (i + 1) n
+    lemCount _ _ = unsafeCoerceRefl
+
+    lemElem :: Elem x ys ~ True => proxy x -> proxy' (y : ys) -> Elem x (y : ys) :~: True
+    lemElem _ _ = unsafeCoerceRefl
+
+    provePerm1 :: Proxy isTop -> SNat (Rank isTop) -> Perm is'
+               -> Maybe (AllElem' is' (Count 0 (Rank isTop)) :~: True)
+    provePerm1 _ _ PNil = Just (Refl)
+    provePerm1 p rtop@SNat (PCons sn@SNat perm)
+      | Just Refl <- provePerm1 p rtop perm
+      = case (cmpNat (SNat @0) sn, cmpNat sn rtop) of
+          (LTI, LTI) | Refl <- lemElemCount sn rtop -> Just Refl
+          (EQI, LTI) | Refl <- lemElemCount sn rtop -> Just Refl
+          _ -> Nothing
+      | otherwise
+      = Nothing
+
+    provePerm2 :: SNat i -> SNat n -> Perm is'
+               -> Maybe (AllElem' (Count i n) is' :~: True)
+    provePerm2 = \i@(SNat :: SNat i) n@SNat perm ->
+      case cmpNat i n of
+        EQI -> Just Refl
+        LTI | Refl <- lemCount i n
+            , Just Refl <- provePerm2 (SNat @(i + 1)) n perm
+            -> checkElem i perm
+            | otherwise -> Nothing
+        GTI -> error "unreachable"
+      where
+        checkElem :: SNat i -> Perm is' -> Maybe (Elem i is' :~: True)
+        checkElem _ PNil = Nothing
+        checkElem i@SNat (PCons k@SNat perm :: Perm is') =
+          case sameNat i k of
+            Just Refl -> Just Refl
+            Nothing | Just Refl <- checkElem i perm, Refl <- lemElem i (Proxy @is') -> Just Refl
+                    | otherwise -> Nothing
+
+    provePermInverse :: Perm is -> Perm is' -> StaticShX sh
+                     -> Maybe (Permute is' (Permute is sh) :~: sh)
+    provePermInverse perm perminv ssh =
+      ssxGeq (ssxPermute perminv (ssxPermute perm ssh)) ssh
+
+type family MapSucc is where
+  MapSucc '[] = '[]
+  MapSucc (i : is) = i + 1 : MapSucc is
+
+permShift1 :: Perm l -> Perm (0 : MapSucc l)
+permShift1 = (SNat @0 `PCons`) . permMapSucc
+  where
+    permMapSucc :: Perm l -> Perm (MapSucc l)
+    permMapSucc PNil = PNil
+    permMapSucc ((SNat :: SNat i) `PCons` ns) = SNat @(i + 1) `PCons` permMapSucc ns
+
+
+-- * Lemmas
+
+lemRankPermute :: Proxy sh -> Perm is -> Rank (Permute is sh) :~: Rank is
+lemRankPermute _ PNil = Refl
+lemRankPermute p (_ `PCons` is) | Refl <- lemRankPermute p is = Refl
+
+lemRankDropLen :: forall is sh. (Rank is <= Rank sh)
+               => StaticShX sh -> Perm is -> Rank (DropLen is sh) :~: Rank sh - Rank is
+lemRankDropLen ZKX PNil = Refl
+lemRankDropLen (_ :!% sh) (_ `PCons` is) | Refl <- lemRankDropLen sh is = Refl
+lemRankDropLen (_ :!% _) PNil = Refl
+lemRankDropLen ZKX (_ `PCons` _) = error "1 <= 0"
+
+lemIndexSucc :: Proxy i -> Proxy a -> Proxy l
+             -> Index (i + 1) (a : l) :~: Index i l
+lemIndexSucc _ _ _ = unsafeCoerceRefl
diff --git a/src/Data/Array/Mixed/Shape.hs b/src/Data/Array/Mixed/Shape.hs
new file mode 100644
index 0000000..a16da76
--- /dev/null
+++ b/src/Data/Array/Mixed/Shape.hs
@@ -0,0 +1,455 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE NoStarIsType #-}
+{-# LANGUAGE PatternSynonyms #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE QuantifiedConstraints #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE RoleAnnotations #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE StandaloneKindSignatures #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE UndecidableInstances #-}
+{-# LANGUAGE ViewPatterns #-}
+{-# OPTIONS_GHC -fplugin GHC.TypeLits.Normalise #-}
+{-# OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver #-}
+module Data.Array.Mixed.Shape where
+
+import Control.DeepSeq (NFData(..))
+import qualified Data.Foldable as Foldable
+import Data.Functor.Const
+import Data.Kind (Type, Constraint)
+import Data.Monoid (Sum(..))
+import Data.Proxy
+import Data.Type.Equality
+import GHC.Generics (Generic)
+import GHC.IsList (IsList)
+import qualified GHC.IsList as IsList
+import GHC.TypeLits
+
+import Data.Array.Mixed.Types
+import Data.Coerce
+import Data.Bifunctor (first)
+
+
+-- | 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
+
+type role ListX nominal representational
+type ListX :: [Maybe Nat] -> (Maybe Nat -> Type) -> Type
+data ListX sh f where
+  ZX :: ListX '[] f
+  (::%) :: f n -> ListX sh f -> ListX (n : sh) f
+deriving instance (forall n. Eq (f n)) => Eq (ListX sh f)
+deriving instance (forall n. Ord (f n)) => Ord (ListX sh f)
+infixr 3 ::%
+
+instance (forall n. Show (f n)) => Show (ListX sh f) where
+  showsPrec _ = listxShow shows
+
+instance (forall n. NFData (f n)) => NFData (ListX sh f) where
+  rnf ZX = ()
+  rnf (x ::% l) = rnf x `seq` rnf l
+
+data UnconsListXRes f sh1 =
+  forall n sh. (n : sh ~ sh1) => UnconsListXRes (ListX sh f) (f n)
+listxUncons :: ListX sh1 f -> Maybe (UnconsListXRes f sh1)
+listxUncons (i ::% shl') = Just (UnconsListXRes shl' i)
+listxUncons ZX = Nothing
+
+listxFmap :: (forall n. f n -> g n) -> ListX sh f -> ListX sh g
+listxFmap _ ZX = ZX
+listxFmap f (x ::% xs) = f x ::% listxFmap f xs
+
+listxFold :: Monoid m => (forall n. f n -> m) -> ListX sh f -> m
+listxFold _ ZX = mempty
+listxFold f (x ::% xs) = f x <> listxFold f xs
+
+listxLength :: ListX sh f -> Int
+listxLength = getSum . listxFold (\_ -> Sum 1)
+
+listxLengthSNat :: ListX sh f -> SNat (Rank sh)
+listxLengthSNat ZX = SNat
+listxLengthSNat (_ ::% l) | SNat <- listxLengthSNat l = SNat
+
+listxShow :: forall sh f. (forall n. f n -> ShowS) -> ListX sh f -> ShowS
+listxShow f l = showString "[" . go "" l . showString "]"
+  where
+    go :: String -> ListX sh' f -> ShowS
+    go _ ZX = id
+    go prefix (x ::% xs) = showString prefix . f x . go "," xs
+
+listxToList :: ListX sh' (Const i) -> [i]
+listxToList ZX = []
+listxToList (Const i ::% is) = i : listxToList is
+
+listxAppend :: ListX sh f -> ListX sh' f -> ListX (sh ++ sh') f
+listxAppend ZX idx' = idx'
+listxAppend (i ::% idx) idx' = i ::% listxAppend idx idx'
+
+listxDrop :: forall f g sh sh'. ListX (sh ++ sh') f -> ListX sh g -> ListX sh' f
+listxDrop long ZX = long
+listxDrop long (_ ::% short) = case long of _ ::% long' -> listxDrop long' short
+
+
+-- * Mixed indices
+
+-- | This is a newtype over 'ListX'.
+type role IxX nominal representational
+type IxX :: [Maybe Nat] -> Type -> Type
+newtype IxX sh i = IxX (ListX sh (Const i))
+  deriving (Eq, Ord, Generic)
+
+pattern ZIX :: forall sh i. () => sh ~ '[] => IxX sh i
+pattern ZIX = IxX ZX
+
+pattern (:.%)
+  :: forall {sh1} {i}.
+     forall n sh. (n : sh ~ sh1)
+  => i -> IxX sh i -> IxX sh1 i
+pattern i :.% shl <- IxX (listxUncons -> Just (UnconsListXRes (IxX -> shl) (getConst -> i)))
+  where i :.% IxX shl = IxX (Const i ::% shl)
+infixr 3 :.%
+
+{-# COMPLETE ZIX, (:.%) #-}
+
+type IIxX sh = IxX sh Int
+
+instance Show i => Show (IxX sh i) where
+  showsPrec _ (IxX l) = listxShow (\(Const i) -> shows i) l
+
+instance Functor (IxX sh) where
+  fmap f (IxX l) = IxX (listxFmap (Const . f . getConst) l)
+
+instance Foldable (IxX sh) where
+  foldMap f (IxX l) = listxFold (f . getConst) l
+
+instance NFData i => NFData (IxX sh i)
+
+ixxZero :: StaticShX sh -> IIxX sh
+ixxZero ZKX = ZIX
+ixxZero (_ :!% ssh) = 0 :.% ixxZero ssh
+
+ixxZero' :: IShX sh -> IIxX sh
+ixxZero' ZSX = ZIX
+ixxZero' (_ :$% sh) = 0 :.% ixxZero' sh
+
+ixxAppend :: forall sh sh' i. IxX sh i -> IxX sh' i -> IxX (sh ++ sh') i
+ixxAppend = coerce (listxAppend @_ @(Const i))
+
+ixxDrop :: forall sh sh' i. IxX (sh ++ sh') i -> IxX sh i -> IxX sh' i
+ixxDrop = coerce (listxDrop @(Const i) @(Const i))
+
+ixxFromLinear :: IShX sh -> Int -> IIxX sh
+ixxFromLinear = \sh i -> case go sh i of
+  (idx, 0) -> idx
+  _ -> error $ "ixxFromLinear: out of range (" ++ show i ++
+               " in array of shape " ++ show sh ++ ")"
+  where
+    -- returns (index in subarray, remaining index in enclosing array)
+    go :: IShX sh -> Int -> (IIxX sh, Int)
+    go ZSX i = (ZIX, i)
+    go (n :$% sh) i =
+      let (idx, i') = go sh i
+          (upi, locali) = i' `quotRem` fromSMayNat' n
+      in (locali :.% idx, upi)
+
+ixxToLinear :: IShX sh -> IIxX sh -> Int
+ixxToLinear = \sh i -> fst (go sh i)
+  where
+    -- returns (index in subarray, size of subarray)
+    go :: IShX sh -> IIxX sh -> (Int, Int)
+    go ZSX ZIX = (0, 1)
+    go (n :$% sh) (i :.% ix) =
+      let (lidx, sz) = go sh ix
+      in (sz * i + lidx, fromSMayNat' n * sz)
+
+
+-- * Mixed shapes
+
+data SMayNat i f n where
+  SUnknown :: i -> SMayNat i f Nothing
+  SKnown :: f n -> SMayNat i f (Just n)
+deriving instance (Show i, forall m. Show (f m)) => Show (SMayNat i f n)
+deriving instance (Eq i, forall m. Eq (f m)) => Eq (SMayNat i f n)
+deriving instance (Ord i, forall m. Ord (f m)) => Ord (SMayNat i f n)
+
+instance (NFData i, forall m. NFData (f m)) => NFData (SMayNat i f n) where
+  rnf (SUnknown i) = rnf i
+  rnf (SKnown x) = rnf x
+
+fromSMayNat :: (n ~ Nothing => i -> r)
+            -> (forall m. n ~ Just m => f m -> r)
+            -> SMayNat i f n -> r
+fromSMayNat f _ (SUnknown i) = f i
+fromSMayNat _ g (SKnown s) = g s
+
+fromSMayNat' :: SMayNat Int SNat n -> Int
+fromSMayNat' = fromSMayNat id fromSNat'
+
+type family AddMaybe n m where
+  AddMaybe Nothing _ = Nothing
+  AddMaybe (Just _) Nothing = Nothing
+  AddMaybe (Just n) (Just m) = Just (n + m)
+
+smnAddMaybe :: SMayNat Int SNat n -> SMayNat Int SNat m -> SMayNat Int SNat (AddMaybe n m)
+smnAddMaybe (SUnknown n) m = SUnknown (n + fromSMayNat' m)
+smnAddMaybe (SKnown n) (SUnknown m) = SUnknown (fromSNat' n + m)
+smnAddMaybe (SKnown n) (SKnown m) = SKnown (snatPlus n m)
+
+
+-- | This is a newtype over 'ListX'.
+type role ShX nominal representational
+type ShX :: [Maybe Nat] -> Type -> Type
+newtype ShX sh i = ShX (ListX sh (SMayNat i SNat))
+  deriving (Eq, Ord, Generic)
+
+pattern ZSX :: forall sh i. () => sh ~ '[] => ShX sh i
+pattern ZSX = ShX ZX
+
+pattern (:$%)
+  :: forall {sh1} {i}.
+     forall n sh. (n : sh ~ sh1)
+  => SMayNat i SNat n -> ShX sh i -> ShX sh1 i
+pattern i :$% shl <- ShX (listxUncons -> Just (UnconsListXRes (ShX -> shl) i))
+  where i :$% ShX shl = ShX (i ::% shl)
+infixr 3 :$%
+
+{-# COMPLETE ZSX, (:$%) #-}
+
+type IShX sh = ShX sh Int
+
+instance Show i => Show (ShX sh i) where
+  showsPrec _ (ShX l) = listxShow (fromSMayNat shows (shows . fromSNat)) l
+
+instance Functor (ShX sh) where
+  fmap f (ShX l) = ShX (listxFmap (fromSMayNat (SUnknown . f) SKnown) l)
+
+instance NFData i => NFData (ShX sh i) where
+  rnf (ShX ZX) = ()
+  rnf (ShX (SUnknown i ::% l)) = rnf i `seq` rnf (ShX l)
+  rnf (ShX (SKnown SNat ::% l)) = rnf (ShX l)
+
+shxLength :: ShX sh i -> Int
+shxLength (ShX l) = listxLength l
+
+-- | This is more than @geq@: it also checks that the integers (the unknown
+-- dimensions) are the same.
+shxEqual :: Eq i => ShX sh i -> ShX sh' i -> Maybe (sh :~: sh')
+shxEqual ZSX ZSX = Just Refl
+shxEqual (SKnown n@SNat :$% sh) (SKnown m@SNat :$% sh')
+  | Just Refl <- sameNat n m
+  , Just Refl <- shxEqual sh sh'
+  = Just Refl
+shxEqual (SUnknown i :$% sh) (SUnknown j :$% sh')
+  | i == j
+  , Just Refl <- shxEqual sh sh'
+  = Just Refl
+shxEqual _ _ = Nothing
+
+-- | The number of elements in an array described by this shape.
+shxSize :: IShX sh -> Int
+shxSize ZSX = 1
+shxSize (n :$% sh) = fromSMayNat' n * shxSize sh
+
+shxToList :: IShX sh -> [Int]
+shxToList ZSX = []
+shxToList (smn :$% sh) = fromSMayNat' smn : shxToList sh
+
+shxAppend :: forall sh sh' i. ShX sh i -> ShX sh' i -> ShX (sh ++ sh') i
+shxAppend = coerce (listxAppend @_ @(SMayNat i SNat))
+
+shxTail :: ShX (n : sh) i -> ShX sh i
+shxTail (_ :$% sh) = sh
+
+shxDropSSX :: forall sh sh' i. ShX (sh ++ sh') i -> StaticShX sh -> ShX sh' i
+shxDropSSX = coerce (listxDrop @(SMayNat i SNat) @(SMayNat () SNat))
+
+shxDropIx :: forall sh sh' i j. ShX (sh ++ sh') i -> IxX sh j -> ShX sh' i
+shxDropIx = coerce (listxDrop @(SMayNat i SNat) @(Const j))
+
+shxDropSh :: forall sh sh' i. ShX (sh ++ sh') i -> ShX sh i -> ShX sh' i
+shxDropSh = coerce (listxDrop @(SMayNat i SNat) @(SMayNat i SNat))
+
+shxTakeSSX :: forall sh sh' i. Proxy sh' -> ShX (sh ++ sh') i -> StaticShX sh -> ShX sh i
+shxTakeSSX _ = flip go
+  where
+    go :: StaticShX sh1 -> ShX (sh1 ++ sh') i -> ShX sh1 i
+    go ZKX _ = ZSX
+    go (_ :!% ssh1) (n :$% sh) = n :$% go ssh1 sh
+
+-- This is a weird operation, so it has a long name
+shxCompleteZeros :: StaticShX sh -> IShX sh
+shxCompleteZeros ZKX = ZSX
+shxCompleteZeros (SUnknown () :!% ssh) = SUnknown 0 :$% shxCompleteZeros ssh
+shxCompleteZeros (SKnown n :!% ssh) = SKnown n :$% shxCompleteZeros ssh
+
+shxSplitApp :: Proxy sh' -> StaticShX sh -> ShX (sh ++ sh') i -> (ShX sh i, ShX sh' i)
+shxSplitApp _ ZKX idx = (ZSX, idx)
+shxSplitApp p (_ :!% ssh) (i :$% idx) = first (i :$%) (shxSplitApp p ssh idx)
+
+shxEnum :: IShX sh -> [IIxX sh]
+shxEnum = \sh -> go sh id []
+  where
+    go :: IShX sh -> (IIxX sh -> a) -> [a] -> [a]
+    go ZSX f = (f ZIX :)
+    go (n :$% sh) f = foldr (.) id [go sh (f . (i :.%)) | i <- [0 .. fromSMayNat' n - 1]]
+
+
+-- * Static mixed shapes
+
+-- | The part of a shape that is statically known. (A newtype over 'ListX'.)
+type StaticShX :: [Maybe Nat] -> Type
+newtype StaticShX sh = StaticShX (ListX sh (SMayNat () SNat))
+  deriving (Eq, Ord)
+
+pattern ZKX :: forall sh. () => sh ~ '[] => StaticShX sh
+pattern ZKX = StaticShX ZX
+
+pattern (:!%)
+  :: forall {sh1}.
+     forall n sh. (n : sh ~ sh1)
+  => SMayNat () SNat n -> StaticShX sh -> StaticShX sh1
+pattern i :!% shl <- StaticShX (listxUncons -> Just (UnconsListXRes (StaticShX -> shl) i))
+  where i :!% StaticShX shl = StaticShX (i ::% shl)
+infixr 3 :!%
+
+{-# COMPLETE ZKX, (:!%) #-}
+
+instance Show (StaticShX sh) where
+  showsPrec _ (StaticShX l) = listxShow (fromSMayNat shows (shows . fromSNat)) l
+
+ssxLength :: StaticShX sh -> Int
+ssxLength (StaticShX l) = listxLength l
+
+-- | This suffices as an implementation of @geq@ in the @Data.GADT.Compare@
+-- class of the @some@ package.
+ssxGeq :: StaticShX sh -> StaticShX sh' -> Maybe (sh :~: sh')
+ssxGeq ZKX ZKX = Just Refl
+ssxGeq (SKnown n@SNat :!% sh) (SKnown m@SNat :!% sh')
+  | Just Refl <- sameNat n m
+  , Just Refl <- ssxGeq sh sh'
+  = Just Refl
+ssxGeq (SUnknown () :!% sh) (SUnknown () :!% sh')
+  | Just Refl <- ssxGeq sh sh'
+  = Just Refl
+ssxGeq _ _ = Nothing
+
+ssxAppend :: StaticShX sh -> StaticShX sh' -> StaticShX (sh ++ sh')
+ssxAppend ZKX sh' = sh'
+ssxAppend (n :!% sh) sh' = n :!% ssxAppend sh sh'
+
+ssxTail :: StaticShX (n : sh) -> StaticShX sh
+ssxTail (_ :!% ssh) = ssh
+
+ssxDropIx :: forall sh sh' i. StaticShX (sh ++ sh') -> IxX sh i -> StaticShX sh'
+ssxDropIx = coerce (listxDrop @(SMayNat () SNat) @(Const i))
+
+-- | This may fail if @sh@ has @Nothing@s in it.
+ssxToShX' :: StaticShX sh -> Maybe (IShX sh)
+ssxToShX' ZKX = Just ZSX
+ssxToShX' (SKnown n :!% sh) = (SKnown n :$%) <$> ssxToShX' sh
+ssxToShX' (SUnknown _ :!% _) = Nothing
+
+ssxReplicate :: SNat n -> StaticShX (Replicate n Nothing)
+ssxReplicate SZ = ZKX
+ssxReplicate (SS (n :: SNat n'))
+  | Refl <- lemReplicateSucc @(Nothing @Nat) @n'
+  = SUnknown () :!% ssxReplicate n
+
+ssxIotaFrom :: Int -> StaticShX sh -> [Int]
+ssxIotaFrom _ ZKX = []
+ssxIotaFrom i (_ :!% ssh) = i : ssxIotaFrom (i+1) ssh
+
+ssxFromShape :: IShX sh -> StaticShX sh
+ssxFromShape ZSX = ZKX
+ssxFromShape (n :$% sh) = fromSMayNat (\_ -> SUnknown ()) SKnown n :!% ssxFromShape sh
+
+
+-- | Evidence for the static part of a shape. This pops up only when you are
+-- polymorphic in the element type of an array.
+type KnownShX :: [Maybe Nat] -> Constraint
+class KnownShX sh where knownShX :: StaticShX sh
+instance KnownShX '[] where knownShX = ZKX
+instance (KnownNat n, KnownShX sh) => KnownShX (Just n : sh) where knownShX = SKnown natSing :!% knownShX
+instance KnownShX sh => KnownShX (Nothing : sh) where knownShX = SUnknown () :!% knownShX
+
+
+-- * Flattening
+
+type Flatten sh = Flatten' 1 sh
+
+type family Flatten' acc sh where
+  Flatten' acc '[] = Just acc
+  Flatten' acc (Nothing : sh) = Nothing
+  Flatten' acc (Just n : sh) = Flatten' (acc * n) sh
+
+-- This function is currently unused
+ssxFlatten :: StaticShX sh -> SMayNat () SNat (Flatten sh)
+ssxFlatten = go (SNat @1)
+  where
+    go :: SNat acc -> StaticShX sh -> SMayNat () SNat (Flatten' acc sh)
+    go acc ZKX = SKnown acc
+    go _ (SUnknown () :!% _) = SUnknown ()
+    go acc (SKnown sn :!% sh) = go (snatMul acc sn) sh
+
+shxFlatten :: IShX sh -> SMayNat Int SNat (Flatten sh)
+shxFlatten = go (SNat @1)
+  where
+    go :: SNat acc -> IShX sh -> SMayNat Int SNat (Flatten' acc sh)
+    go acc ZSX = SKnown acc
+    go acc (SUnknown n :$% sh) = SUnknown (goUnknown (fromSNat' acc * n) sh)
+    go acc (SKnown sn :$% sh) = go (snatMul acc sn) sh
+
+    goUnknown :: Int -> IShX sh -> Int
+    goUnknown acc ZSX = acc
+    goUnknown acc (SUnknown n :$% sh) = goUnknown (acc * n) sh
+    goUnknown acc (SKnown sn :$% sh) = goUnknown (acc * fromSNat' sn) sh
+
+
+-- | Very untyped: only length is checked (at runtime).
+instance KnownShX sh => IsList (ListX sh (Const i)) where
+  type Item (ListX sh (Const i)) = i
+  fromList topl = go (knownShX @sh) topl
+    where
+      go :: StaticShX sh' -> [i] -> ListX sh' (Const i)
+      go ZKX [] = ZX
+      go (_ :!% sh) (i : is) = Const i ::% go sh is
+      go _ _ = error $ "IsList(ListX): Mismatched list length (type says "
+                         ++ show (ssxLength (knownShX @sh)) ++ ", list has length "
+                         ++ show (length topl) ++ ")"
+  toList = listxToList
+
+-- | Very untyped: only length is checked (at runtime), index bounds are __not checked__.
+instance KnownShX sh => IsList (IxX sh i) where
+  type Item (IxX sh i) = i
+  fromList = IxX . IsList.fromList
+  toList = Foldable.toList
+
+-- | Untyped: length and known dimensions are checked (at runtime).
+instance KnownShX sh => IsList (ShX sh Int) where
+  type Item (ShX sh Int) = Int
+  fromList topl = ShX (go (knownShX @sh) topl)
+    where
+      go :: StaticShX sh' -> [Int] -> ListX sh' (SMayNat Int SNat)
+      go ZKX [] = ZX
+      go (SKnown sn :!% sh) (i : is)
+        | i == fromSNat' sn = SKnown sn ::% go sh is
+        | otherwise = error $ "IsList(ShX): Value does not match typing (type says "
+                                ++ show (fromSNat' sn) ++ ", list contains " ++ show i ++ ")"
+      go (SUnknown () :!% sh) (i : is) = SUnknown i ::% go sh is
+      go _ _ = error $ "IsList(ShX): Mismatched list length (type says "
+                         ++ show (ssxLength (knownShX @sh)) ++ ", list has length "
+                         ++ show (length topl) ++ ")"
+  toList = shxToList
diff --git a/src/Data/Array/Mixed/Types.hs b/src/Data/Array/Mixed/Types.hs
new file mode 100644
index 0000000..d77513f
--- /dev/null
+++ b/src/Data/Array/Mixed/Types.hs
@@ -0,0 +1,110 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE NoStarIsType #-}
+{-# LANGUAGE PatternSynonyms #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE UndecidableInstances #-}
+{-# LANGUAGE ViewPatterns #-}
+{-# OPTIONS_GHC -fplugin GHC.TypeLits.Normalise #-}
+{-# OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver #-}
+module Data.Array.Mixed.Types (
+  -- * Reified evidence of a type class
+  Dict(..),
+
+  -- * Type-level naturals
+  pattern SZ, pattern SS,
+  fromSNat',
+  snatPlus, snatMul,
+
+  -- * Type-level lists
+  type (++),
+  lemAppNil,
+  lemAppAssoc,
+  Replicate,
+  lemReplicateSucc,
+
+  -- * Unsafe
+  unsafeCoerceRefl,
+) where
+
+import Data.Type.Equality
+import Data.Proxy
+import GHC.TypeLits
+import qualified GHC.TypeNats as TN
+import qualified Unsafe.Coerce
+
+
+-- | Evidence for the constraint @c a@.
+data Dict c a where
+  Dict :: c a => Dict c a
+
+fromSNat' :: SNat n -> Int
+fromSNat' = fromIntegral . fromSNat
+
+pattern SZ :: () => (n ~ 0) => SNat n
+pattern SZ <- ((\sn -> testEquality sn (SNat @0)) -> Just Refl)
+  where SZ = SNat
+
+pattern SS :: forall np1. () => forall n. (n + 1 ~ np1) => SNat n -> SNat np1
+pattern SS sn <- (snatPred -> Just (SNatPredResult sn Refl))
+  where SS = snatSucc
+
+{-# COMPLETE SZ, SS #-}
+
+snatSucc :: SNat n -> SNat (n + 1)
+snatSucc SNat = SNat
+
+data SNatPredResult np1 = forall n. SNatPredResult (SNat n) (n + 1 :~: np1)
+snatPred :: forall np1. SNat np1 -> Maybe (SNatPredResult np1)
+snatPred snp1 =
+  withKnownNat snp1 $
+    case cmpNat (Proxy @1) (Proxy @np1) of
+      LTI -> Just (SNatPredResult (SNat @(np1 - 1)) Refl)
+      EQI -> Just (SNatPredResult (SNat @(np1 - 1)) Refl)
+      GTI -> Nothing
+
+-- This should be a function in base
+snatPlus :: SNat n -> SNat m -> SNat (n + m)
+snatPlus n m = TN.withSomeSNat (TN.fromSNat n + TN.fromSNat m) Unsafe.Coerce.unsafeCoerce
+
+-- This should be a function in base
+snatMul :: SNat n -> SNat m -> SNat (n * m)
+snatMul n m = TN.withSomeSNat (TN.fromSNat n * TN.fromSNat m) Unsafe.Coerce.unsafeCoerce
+
+
+-- | This is just @'Unsafe.Coerce.unsafeCoerce' 'Refl'@, but specialised to
+-- only typecheck for actual type equalities. One cannot, e.g. accidentally
+-- write this:
+--
+-- @
+-- foo :: Proxy a -> Proxy b -> a :~: b
+-- foo = unsafeCoerceRefl
+-- @
+--
+-- which would have been permitted with normal 'Unsafe.Coerce.unsafeCoerce',
+-- but would have resulted in interesting memory errors at runtime.
+unsafeCoerceRefl :: a :~: b
+unsafeCoerceRefl = Unsafe.Coerce.unsafeCoerce Refl
+
+
+-- | Type-level list append.
+type family l1 ++ l2 where
+  '[] ++ l2 = l2
+  (x : xs) ++ l2 = x : xs ++ l2
+
+lemAppNil :: l ++ '[] :~: l
+lemAppNil = unsafeCoerceRefl
+
+lemAppAssoc :: Proxy a -> Proxy b -> Proxy c -> (a ++ b) ++ c :~: a ++ (b ++ c)
+lemAppAssoc _ _ _ = unsafeCoerceRefl
+
+type family Replicate n a where
+  Replicate 0 a = '[]
+  Replicate n a = a : Replicate (n - 1) a
+
+lemReplicateSucc :: (a : Replicate n a) :~: Replicate (n + 1) a
+lemReplicateSucc = unsafeCoerceRefl
-- 
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