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{-# OPTIONS --without-K --safe #-}
module Data.Vector where
open import Data.Nat.Base using (ℕ)
open import Data.Vec.Functional using (Vector; head; tail; []; removeAt; map) public
open import Relation.Binary.PropositionalEquality as ≡ using (_≡_; _≗_)
open import Function.Base using (∣_⟩-_; _∘_)
open import Data.Fin.Base using (Fin; toℕ)
open ℕ
open Fin
foldl
: ∀ {n : ℕ} {A : Set} (B : ℕ → Set)
→ (∀ {k : Fin n} → B (toℕ k) → A → B (suc (toℕ k)))
→ B zero
→ Vector A n
→ B n
foldl {zero} B ⊕ e v = e
foldl {suc n} B ⊕ e v = foldl (B ∘ suc) ⊕ (⊕ e (head v)) (tail v)
foldl-cong
: {n : ℕ} {A : Set}
(B : ℕ → Set)
{f g : ∀ {k : Fin n} → B (toℕ k) → A → B (suc (toℕ k))}
→ (∀ {k} → ∀ x y → f {k} x y ≡ g {k} x y)
→ (e : B zero)
→ (v : Vector A n)
→ foldl B f e v ≡ foldl B g e v
foldl-cong {zero} B f≗g e v = ≡.refl
foldl-cong {suc n} B {g = g} f≗g e v rewrite (f≗g e (head v)) = foldl-cong (B ∘ suc) f≗g (g e (head v)) (tail v)
foldl-cong-arg
: {n : ℕ} {A : Set}
(B : ℕ → Set)
(f : ∀ {k : Fin n} → B (toℕ k) → A → B (suc (toℕ k)))
→ (e : B zero)
→ {v w : Vector A n}
→ v ≗ w
→ foldl B f e v ≡ foldl B f e w
foldl-cong-arg {zero} B f e v≗w = ≡.refl
foldl-cong-arg {suc n} B f e {w = w} v≗w rewrite v≗w zero = foldl-cong-arg (B ∘ suc) f (f e (head w)) (v≗w ∘ suc)
foldl-map
: {n : ℕ} {A : ℕ → Set} {B C : Set}
(f : ∀ {k : Fin n} → A (toℕ k) → B → A (suc (toℕ k)))
(g : C → B)
(x : A zero)
(xs : Vector C n)
→ foldl A f x (map g xs)
≡ foldl A (∣ f ⟩- g) x xs
foldl-map {zero} f g e xs = ≡.refl
foldl-map {suc n} f g e xs = foldl-map f g (f e (g (head xs))) (tail xs)
foldl-fusion
: {n : ℕ}
{A : Set} {B C : ℕ → Set}
(h : {k : ℕ} → B k → C k)
→ {f : {k : Fin n} → B (toℕ k) → A → B (suc (toℕ k))} {d : B zero}
→ {g : {k : Fin n} → C (toℕ k) → A → C (suc (toℕ k))} {e : C zero}
→ (h d ≡ e)
→ ({k : Fin n} (b : B (toℕ k)) (x : A) → h (f {k} b x) ≡ g (h b) x)
→ h ∘ foldl B f d ≗ foldl C g e
foldl-fusion {zero} _ base _ _ = base
foldl-fusion {suc n} {A} h {f} {d} {g} {e} base fuse xs = foldl-fusion h eq fuse (tail xs)
where
x₀ : A
x₀ = head xs
open ≡.≡-Reasoning
eq : h (f d x₀) ≡ g e x₀
eq = begin
h (f d x₀) ≡⟨ fuse d x₀ ⟩
g (h d) x₀ ≡⟨ ≡.cong-app (≡.cong g base) x₀ ⟩
g e x₀ ∎
foldl-[]
: {A : Set}
(B : ℕ → Set)
(f : {k : Fin 0} → B (toℕ k) → A → B (suc (toℕ k)))
{e : B 0}
→ foldl B f e [] ≡ e
foldl-[] _ _ = ≡.refl
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