68 lines
3.4 KiB
Agda
68 lines
3.4 KiB
Agda
-- Because iterated products currently require both A and B to be of the same
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-- universe, and the FiniteMap is written in a universe-polymorphic way,
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-- specialize the FiniteMap module with Set-typed types only.
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open import Lattice
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open import Equivalence
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open import Relation.Binary.PropositionalEquality as Eq using (_≡_; refl; sym; trans; cong; subst)
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open import Relation.Binary.Definitions using (Decidable)
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open import Agda.Primitive using (Level) renaming (_⊔_ to _⊔ℓ_)
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open import Function.Definitions using (Inverseˡ; Inverseʳ)
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module Lattice.FiniteValueMap (A : Set) (B : Set)
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(_≈₂_ : B → B → Set)
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(_⊔₂_ : B → B → B) (_⊓₂_ : B → B → B)
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(≈-dec-A : Decidable (_≡_ {_} {A}))
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(lB : IsLattice B _≈₂_ _⊔₂_ _⊓₂_) where
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open import Data.List using (List; length; []; _∷_)
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open import Utils using (Unique; push; empty)
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open import Data.Product using (_,_)
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open import Data.List.Properties using (∷-injectiveʳ)
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open import Data.List.Relation.Unary.All using (All)
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open import Relation.Nullary using (¬_)
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open import Lattice.FiniteMap A B _≈₂_ _⊔₂_ _⊓₂_ ≈-dec-A lB public
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module IterProdIsomorphism where
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open import Data.Unit using (⊤; tt)
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open import Lattice.Unit using () renaming (_≈_ to _≈ᵘ_; _⊔_ to _⊔ᵘ_; _⊓_ to _⊓ᵘ_; ≈-dec to ≈ᵘ-dec; isLattice to isLatticeᵘ)
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open import Lattice.IterProd _≈₂_ _≈ᵘ_ _⊔₂_ _⊔ᵘ_ _⊓₂_ _⊓ᵘ_ lB isLatticeᵘ as IP using (IterProd)
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from : ∀ {ks : List A} → FiniteMap ks → IterProd (length ks)
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from {[]} (([] , _) , _) = tt
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from {k ∷ ks'} (((k' , v) ∷ kvs' , push _ uks') , refl) = (v , from ((kvs' , uks'), refl))
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to : ∀ {ks : List A} → Unique ks → IterProd (length ks) → FiniteMap ks
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to {[]} _ ⊤ = (([] , empty) , refl)
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to {k ∷ ks'} (push k≢ks' uks') (v , rest)
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with to uks' rest
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... | ((kvs' , ukvs') , kvs'≡ks') =
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let
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-- This would be easier if we pattern matched on the equiality proof
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-- to get refl, but that makes it harder to reason about 'to' when
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-- the arguments are not known to be refl.
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k≢kvs' = subst (λ ks → All (λ k' → ¬ k ≡ k') ks) (sym kvs'≡ks') k≢ks'
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kvs≡ks = cong (k ∷_) kvs'≡ks'
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in
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(((k , v) ∷ kvs' , push k≢kvs' ukvs') , kvs≡ks)
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private
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_≈ᵐ_ : ∀ {ks : List A} → FiniteMap ks → FiniteMap ks → Set
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_≈ᵐ_ {ks} = _≈_ ks
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_≈ⁱᵖ_ : ∀ {ks : List A} → IterProd (length ks) → IterProd (length ks) → Set
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_≈ⁱᵖ_ {ks} = IP._≈_ (length ks)
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from-to-inverseˡ : ∀ {ks : List A} (uks : Unique ks) →
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Inverseˡ (_≈ᵐ_ {ks}) (_≈ⁱᵖ_ {ks}) (from {ks}) (to {ks} uks) -- from (to x) = x
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from-to-inverseˡ {[]} _ _ = IsEquivalence.≈-refl (IP.≈-equiv 0)
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from-to-inverseˡ {k ∷ ks'} (push k≢ks' uks') (v , rest)
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with ((kvs' , ukvs') , refl) ← to uks' rest in p rewrite sym p =
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(IsLattice.≈-refl lB , from-to-inverseˡ {ks'} uks' rest)
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-- the rewrite here is needed because the IH is in terms of `to uks' rest`,
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-- but we end up with the 'unpacked' form (kvs', ...). So, put it back
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-- in the 'packed' form after we've performed enough inspection
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-- to know we take the cons branch of `to`.
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