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{-# LANGUAGE DataKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE TypeOperators #-}
{-# OPTIONS_GHC -fplugin GHC.TypeLits.Normalise #-}
{-# OPTIONS_GHC -fplugin GHC.TypeLits.KnownNat.Solver #-}
module Data.Array.Mixed.Lemmas where
import Data.Proxy
import Data.Type.Equality
import GHC.TypeLits
import Data.Array.Mixed.Permutation
import Data.Array.Mixed.Shape
import Data.Array.Mixed.Types
-- * Reasoning helpers
subst1 :: forall f a b. a :~: b -> f a :~: f b
subst1 Refl = Refl
subst2 :: forall f c a b. a :~: b -> f a c :~: f b c
subst2 Refl = Refl
-- * Lemmas
-- ** Nat
lemLeqSuccSucc :: (k + 1 <= n) => Proxy k -> Proxy n -> (k <=? n - 1) :~: True
lemLeqSuccSucc _ _ = unsafeCoerceRefl
lemLeqPlus :: n <= m => Proxy n -> Proxy m -> Proxy k -> (n <=? (m + k)) :~: 'True
lemLeqPlus _ _ _ = Refl
-- ** Append
lemAppNil :: l ++ '[] :~: l
lemAppNil = unsafeCoerceRefl
lemAppAssoc :: Proxy a -> Proxy b -> Proxy c -> (a ++ b) ++ c :~: a ++ (b ++ c)
lemAppAssoc _ _ _ = unsafeCoerceRefl
lemAppLeft :: Proxy l -> a :~: b -> a ++ l :~: b ++ l
lemAppLeft _ Refl = Refl
-- ** Rank
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
lemRankReplicate :: SNat n -> Rank (Replicate n (Nothing @Nat)) :~: n
lemRankReplicate SZ = Refl
lemRankReplicate (SS (n :: SNat nm1))
| Refl <- lemReplicateSucc @(Nothing @Nat) @nm1
, Refl <- lemRankReplicate n
= Refl
-- ** Various type families
lemReplicatePlusApp :: forall n m a. SNat n -> Proxy m -> Proxy a
-> Replicate (n + m) a :~: Replicate n a ++ Replicate m a
lemReplicatePlusApp sn _ _ = go sn
where
go :: SNat n' -> Replicate (n' + m) a :~: Replicate n' a ++ Replicate m a
go SZ = Refl
go (SS (n :: SNat n'm1))
| Refl <- lemReplicateSucc @a @n'm1
, Refl <- go n
= sym (lemReplicateSucc @a @(n'm1 + m))
lemDropLenApp :: Rank l1 <= Rank l2
=> Proxy l1 -> Proxy l2 -> Proxy rest
-> DropLen l1 l2 ++ rest :~: DropLen l1 (l2 ++ rest)
lemDropLenApp _ _ _ = unsafeCoerceRefl
lemTakeLenApp :: Rank l1 <= Rank l2
=> Proxy l1 -> Proxy l2 -> Proxy rest
-> TakeLen l1 l2 :~: TakeLen l1 (l2 ++ rest)
lemTakeLenApp _ _ _ = unsafeCoerceRefl
lemInitApp :: Proxy l -> Proxy x -> Init (l ++ '[x]) :~: l
lemInitApp _ _ = unsafeCoerceRefl
-- ** KnownNat
lemKnownNatSucc :: KnownNat n => Dict KnownNat (n + 1)
lemKnownNatSucc = Dict
lemKnownNatRank :: ShX sh i -> 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
-- ** Known shapes
lemKnownReplicate :: SNat n -> Dict KnownShX (Replicate n Nothing)
lemKnownReplicate sn = lemKnownShX (ssxFromSNat sn)
lemKnownShX :: StaticShX sh -> Dict KnownShX sh
lemKnownShX ZKX = Dict
lemKnownShX (SKnown SNat :!% ssh) | Dict <- lemKnownShX ssh = Dict
lemKnownShX (SUnknown () :!% ssh) | Dict <- lemKnownShX ssh = Dict
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