------------------------------------------------------------------------ -- The Agda standard library -- -- The Colist type and some operations ------------------------------------------------------------------------ {-# OPTIONS --without-K --safe --sized-types #-} module Codata.Colist where open import Level using (Level) open import Size open import Data.Unit open import Data.Nat.Base open import Data.Product using (_×_ ; _,_) open import Data.These.Base using (These; this; that; these) open import Data.Maybe.Base using (Maybe; nothing; just) open import Data.List.Base using (List; []; _∷_) open import Data.List.NonEmpty as List⁺ using (List⁺; _∷_) open import Data.Vec.Base as Vec using (Vec; []; _∷_) open import Data.Vec.Bounded as Vec≤ using (Vec≤) open import Function open import Codata.Thunk using (Thunk; force) open import Codata.Conat as Conat using (Conat ; zero ; suc) open import Codata.Cowriter as CW using (Cowriter; _∷_) open import Codata.Delay as Delay using (Delay ; now ; later) open import Codata.Stream using (Stream ; _∷_) open import Relation.Binary.PropositionalEquality using (_≡_; refl) private variable a b c w : Level i : Size A : Set a B : Set b C : Set c W : Set w data Colist (A : Set a) (i : Size) : Set a where [] : Colist A i _∷_ : A → Thunk (Colist A) i → Colist A i ------------------------------------------------------------------------ -- Relationship to Cowriter. fromCowriter : Cowriter W A i → Colist W i fromCowriter CW.[ _ ] = [] fromCowriter (w ∷ ca) = w ∷ λ where .force → fromCowriter (ca .force) toCowriter : Colist A i → Cowriter A ⊤ i toCowriter [] = CW.[ _ ] toCowriter (a ∷ as) = a ∷ λ where .force → toCowriter (as .force) ------------------------------------------------------------------------ -- Basic functions. [_] : A → Colist A ∞ [ a ] = a ∷ λ where .force → [] length : Colist A i → Conat i length [] = zero length (x ∷ xs) = suc λ where .force → length (xs .force) replicate : Conat i → A → Colist A i replicate zero a = [] replicate (suc n) a = a ∷ λ where .force → replicate (n .force) a infixr 5 _++_ _⁺++_ _++_ : Colist A i → Colist A i → Colist A i [] ++ ys = ys (x ∷ xs) ++ ys = x ∷ λ where .force → xs .force ++ ys lookup : ℕ → Colist A ∞ → Maybe A lookup n [] = nothing lookup zero (a ∷ as) = just a lookup (suc n) (a ∷ as) = lookup n (as .force) colookup : Conat i → Colist A i → Delay (Maybe A) i colookup n [] = now nothing colookup zero (a ∷ as) = now (just a) colookup (suc n) (a ∷ as) = later λ where .force → colookup (n .force) (as .force) take : (n : ℕ) → Colist A ∞ → Vec≤ A n take zero xs = Vec≤.[] take n [] = Vec≤.[] take (suc n) (x ∷ xs) = x Vec≤.∷ take n (xs .force) cotake : Conat i → Stream A i → Colist A i cotake zero xs = [] cotake (suc n) (x ∷ xs) = x ∷ λ where .force → cotake (n .force) (xs .force) drop : ℕ → Colist A ∞ → Colist A ∞ drop zero xs = xs drop (suc n) [] = [] drop (suc n) (x ∷ xs) = drop n (xs .force) fromList : List A → Colist A ∞ fromList [] = [] fromList (x ∷ xs) = x ∷ λ where .force → fromList xs fromList⁺ : List⁺ A → Colist A ∞ fromList⁺ = fromList ∘′ List⁺.toList _⁺++_ : List⁺ A → Thunk (Colist A) i → Colist A i (x ∷ xs) ⁺++ ys = x ∷ λ where .force → fromList xs ++ ys .force concat : Colist (List⁺ A) i → Colist A i concat [] = [] concat (as ∷ ass) = as ⁺++ λ where .force → concat (ass .force) fromStream : Stream A i → Colist A i fromStream = cotake Conat.infinity module ChunksOf (n : ℕ) where chunksOf : Colist A ∞ → Cowriter (Vec A n) (Vec≤ A n) i chunksOfAcc : ∀ m → -- We have two continuations but we are only ever going to use one. -- If we had linear types, we'd write the type using the & conjunction here. (k≤ : Vec≤ A m → Vec≤ A n) → (k≡ : Vec A m → Vec A n) → -- Finally we chop up the input stream. Colist A ∞ → Cowriter (Vec A n) (Vec≤ A n) i chunksOf = chunksOfAcc n id id chunksOfAcc zero k≤ k≡ as = k≡ [] ∷ λ where .force → chunksOf as chunksOfAcc (suc k) k≤ k≡ [] = CW.[ k≤ Vec≤.[] ] chunksOfAcc (suc k) k≤ k≡ (a ∷ as) = chunksOfAcc k (k≤ ∘ (a Vec≤.∷_)) (k≡ ∘ (a ∷_)) (as .force) open ChunksOf using (chunksOf) public -- Test to make sure that the values are kept in the same order _ : chunksOf 3 (fromList (1 ∷ 2 ∷ 3 ∷ 4 ∷ [])) ≡ (1 ∷ 2 ∷ 3 ∷ []) ∷ _ _ = refl map : (A → B) → Colist A i → Colist B i map f [] = [] map f (a ∷ as) = f a ∷ λ where .force → map f (as .force) unfold : (A → Maybe (A × B)) → A → Colist B i unfold next seed with next seed ... | nothing = [] ... | just (seed′ , b) = b ∷ λ where .force → unfold next seed′ scanl : (B → A → B) → B → Colist A i → Colist B i scanl c n [] = n ∷ λ where .force → [] scanl c n (a ∷ as) = n ∷ λ where .force → scanl c (c n a) (as .force) alignWith : (These A B → C) → Colist A i → Colist B i → Colist C i alignWith f [] bs = map (f ∘′ that) bs alignWith f as@(_ ∷ _) [] = map (f ∘′ this) as alignWith f (a ∷ as) (b ∷ bs) = f (these a b) ∷ λ where .force → alignWith f (as .force) (bs .force) zipWith : (A → B → C) → Colist A i → Colist B i → Colist C i zipWith f [] bs = [] zipWith f as [] = [] zipWith f (a ∷ as) (b ∷ bs) = f a b ∷ λ where .force → zipWith f (as .force) (bs .force) align : Colist A i → Colist B i → Colist (These A B) i align = alignWith id zip : Colist A i → Colist B i → Colist (A × B) i zip = zipWith _,_ ap : Colist (A → B) i → Colist A i → Colist B i ap = zipWith _$′_