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Universal
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module Universal where | |
open import Relation.Binary.PropositionalEquality | |
open import Relation.Binary | |
open Relation.Binary.PropositionalEquality.≡-Reasoning | |
open import Agda.Primitive | |
open import Data.Nat hiding (_⊔_) | |
open import Data.Unit hiding (setoid) | |
open import Data.Bool | |
open import Data.Nat.Properties | |
open import Data.Product hiding (map) | |
open import Data.Vec hiding (drop; map) | |
open import Data.Fin hiding (_+_) | |
open import Data.List hiding (zipWith) | |
data HVec {a} : (n : ℕ) → List (Set a) → Set a where | |
hnil : HVec 0 [] | |
hcons : {A : Set a} → {n : ℕ} → {l : List (Set a)} → | |
(x : A) → HVec n l → HVec (suc n) (A ∷ l) | |
hLookup : {a : Level} → ∀ {len l} → HVec {a} len l → (n : Fin (length l)) → (lookup n (fromList l)) | |
hLookup hnil () | |
hLookup (hcons x xs) zero = x | |
hLookup (hcons x xs) (suc n) = hLookup xs n | |
opSignature : ∀ {a} → Set a → ℕ → Set a | |
opSignature A zero = A | |
opSignature A (suc n) = A → (opSignature A n) | |
apply : ∀ {a} → {A : Set a} → (n : ℕ) → (f : opSignature A n) → | |
(v : Vec A n) → A | |
apply zero f [] = f | |
apply (suc n) f (x ∷ l) = apply n (f x) l | |
data WellDefined {a b} {A : Set a} (_==_ : A → A → Set b) (n : ℕ) (f : opSignature A n) : Set (a ⊔ b) where | |
wd : ((vx vy : Vec A n) → | |
(p : let t = toList (zipWith _==_ vx vy) in HVec (length t) t) → | |
(apply n f vx == apply n f vy)) → | |
WellDefined _==_ n f | |
respect : ∀ {a b} → {A : Set a} → (_==_ : A → A → Set b) → | |
(ns : List ℕ) → HVec (length ns) (map (opSignature A) ns) → | |
List (Set (a ⊔ b)) | |
respect _ [] _ = [] | |
respect _==_ (n ∷ ns) (hcons f hfs) = (WellDefined _==_ n f) ∷ (respect _==_ ns hfs) | |
open Agda.Primitive | |
record Universal {a b} (S : Setoid a b) (Signature : List ℕ) : Set (lsuc (a ⊔ b)) where | |
open Setoid S | |
n = length Signature | |
opTypes = map (opSignature Carrier) Signature | |
field | |
Operators : HVec n opTypes | |
wdTypes = respect _≈_ Signature Operators | |
field | |
WellDef : HVec n wdTypes | |
record Monoid {a b} (S : Setoid a b) : Set (lsuc (a ⊔ b)) where | |
open Setoid S | |
field | |
{{Uni}} : Universal S (2 ∷ 0 ∷ []) | |
open Universal Uni | |
_●_ = hLookup Operators zero | |
ε = hLookup Operators (suc zero) | |
field | |
assoc : (x y z : Carrier) → (x ● (y ● z)) ≈ ((x ● y) ● z) | |
lunit : (x : Carrier) → (ε ● x) ≈ x | |
runit : (x : Carrier) → (x ● ε) ≈ x | |
plusAssoc : (x y z : ℕ) → x + (y + z) ≡ (x + y) + z | |
plusAssoc zero y z = refl | |
plusAssoc (suc x) y z = cong suc (plusAssoc x y z) | |
plusZero : (x : ℕ) → x + 0 ≡ x | |
plusZero zero = refl | |
plusZero (suc n) = cong suc (plusZero n) | |
plusWellDef : WellDefined _≡_ 2 _+_ | |
plusWellDef = wd f where | |
f : (vx vy : Vec ℕ 2) → | |
let t = toList (zipWith _≡_ vx vy) in HVec (length t) t → | |
apply 2 _+_ vx ≡ apply 2 _+_ vy | |
f (a ∷ b ∷ []) (c ∷ d ∷ []) (hcons pac (hcons pbd hnil)) = | |
begin | |
a + b | |
≡⟨ cong (λ x → x + b) pac ⟩ | |
c + b | |
≡⟨ cong (λ x → c + x) pbd ⟩ | |
c + d | |
∎ | |
zeroWellDef : WellDefined _≡_ 0 0 | |
zeroWellDef = wd f where | |
f : (vx vy : Vec ℕ 0) → | |
let t = toList (zipWith _≡_ vx vy) in HVec (length t) t → | |
apply 0 0 vx ≡ apply 0 0 vy | |
f [] [] _ = refl | |
instance | |
natPlus : Monoid (setoid ℕ) | |
natPlus = record | |
{ | |
Uni = record | |
{ | |
Operators = hcons _+_ (hcons 0 hnil); | |
WellDef = hcons plusWellDef (hcons zeroWellDef hnil) | |
}; | |
assoc = plusAssoc; | |
lunit = λ x → refl; | |
runit = plusZero | |
} | |
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