------------------------------------------------------------------------ -- The Agda standard library -- -- Lists where at least one element satisfies a given property ------------------------------------------------------------------------ module Data.List.Any where open import Data.Empty open import Data.Fin open import Function open import Function.Equality using (_⟨$⟩_) open import Function.Equivalence as Equiv using (module Equivalence) open import Function.Related as Related hiding (_∼[_]_) open import Data.List.Base as List using (List; []; _∷_) open import Data.Product as Prod using (∃; _×_; _,_) open import Level using (Level; _⊔_) open import Relation.Nullary import Relation.Nullary.Decidable as Dec open import Relation.Unary using (Decidable) renaming (_⊆_ to _⋐_) open import Relation.Binary hiding (Decidable) import Relation.Binary.InducedPreorders as Ind open import Relation.Binary.List.Pointwise as ListEq using ([]; _∷_) open import Relation.Binary.PropositionalEquality as PropEq using (_≡_) -- Any P xs means that at least one element in xs satisfies P. data Any {a p} {A : Set a} (P : A → Set p) : List A → Set (a ⊔ p) where here : ∀ {x xs} (px : P x) → Any P (x ∷ xs) there : ∀ {x xs} (pxs : Any P xs) → Any P (x ∷ xs) -- Map. map : ∀ {a p q} {A : Set a} {P : A → Set p} → {Q : A → Set q} → P ⋐ Q → Any P ⋐ Any Q map g (here px) = here (g px) map g (there pxs) = there (map g pxs) -- If the head does not satisfy the predicate, then the tail will. tail : ∀ {a p} {A : Set a} {x : A} {xs : List A} {P : A → Set p} → ¬ P x → Any P (x ∷ xs) → Any P xs tail ¬px (here px) = ⊥-elim (¬px px) tail ¬px (there pxs) = pxs -- Decides Any. any : ∀ {a p} {A : Set a} {P : A → Set p} → Decidable P → Decidable (Any P) any p [] = no λ() any p (x ∷ xs) with p x any p (x ∷ xs) | yes px = yes (here px) any p (x ∷ xs) | no ¬px = Dec.map′ there (tail ¬px) (any p xs) -- index x∈xs is the list position (zero-based) which x∈xs points to. index : ∀ {a p} {A : Set a} {P : A → Set p} {xs} → Any P xs → Fin (List.length xs) index (here px) = zero index (there pxs) = suc (index pxs) ------------------------------------------------------------------------ -- List membership and some related definitions module Membership {c ℓ : Level} (S : Setoid c ℓ) where private open module S = Setoid S using (_≈_) renaming (Carrier to A) open module LS = Setoid (ListEq.setoid S) using () renaming (_≈_ to _≋_) -- If a predicate P respects the underlying equality then Any P -- respects the list equality. lift-resp : ∀ {p} {P : A → Set p} → P Respects _≈_ → Any P Respects _≋_ lift-resp resp [] () lift-resp resp (x≈y ∷ xs≈ys) (here px) = here (resp x≈y px) lift-resp resp (x≈y ∷ xs≈ys) (there pxs) = there (lift-resp resp xs≈ys pxs) -- List membership. infix 4 _∈_ _∉_ _∈_ : A → List A → Set _ x ∈ xs = Any (_≈_ x) xs _∉_ : A → List A → Set _ x ∉ xs = ¬ x ∈ xs -- Subsets. infix 4 _⊆_ _⊈_ _⊆_ : List A → List A → Set _ xs ⊆ ys = ∀ {x} → x ∈ xs → x ∈ ys _⊈_ : List A → List A → Set _ xs ⊈ ys = ¬ xs ⊆ ys -- Equality is respected by the predicate which is used to define -- _∈_. ∈-resp-≈ : ∀ {x} → (_≈_ x) Respects _≈_ ∈-resp-≈ = flip S.trans -- List equality is respected by _∈_. ∈-resp-list-≈ : ∀ {x} → _∈_ x Respects _≋_ ∈-resp-list-≈ = lift-resp ∈-resp-≈ -- _⊆_ is a preorder. ⊆-preorder : Preorder _ _ _ ⊆-preorder = Ind.InducedPreorder₂ (ListEq.setoid S) _∈_ ∈-resp-list-≈ module ⊆-Reasoning where import Relation.Binary.PreorderReasoning as PreR open PreR ⊆-preorder public renaming (_∼⟨_⟩_ to _⊆⟨_⟩_) infix 1 _∈⟨_⟩_ _∈⟨_⟩_ : ∀ x {xs ys} → x ∈ xs → xs IsRelatedTo ys → x ∈ ys x ∈⟨ x∈xs ⟩ xs⊆ys = (begin xs⊆ys) x∈xs -- A variant of List.map. map-with-∈ : ∀ {b} {B : Set b} (xs : List A) → (∀ {x} → x ∈ xs → B) → List B map-with-∈ [] f = [] map-with-∈ (x ∷ xs) f = f (here S.refl) ∷ map-with-∈ xs (f ∘ there) -- Finds an element satisfying the predicate. find : ∀ {p} {P : A → Set p} {xs} → Any P xs → ∃ λ x → x ∈ xs × P x find (here px) = (_ , here S.refl , px) find (there pxs) = Prod.map id (Prod.map there id) (find pxs) lose : ∀ {p} {P : A → Set p} {x xs} → P Respects _≈_ → x ∈ xs → P x → Any P xs lose resp x∈xs px = map (flip resp px) x∈xs -- The code above instantiated (and slightly changed) for -- propositional equality, along with some additional definitions. module Membership-≡ where private open module M {a} {A : Set a} = Membership (PropEq.setoid A) public hiding (lift-resp; lose; ⊆-preorder; module ⊆-Reasoning) lose : ∀ {a p} {A : Set a} {P : A → Set p} {x xs} → x ∈ xs → P x → Any P xs lose {P = P} = M.lose (PropEq.subst P) -- _⊆_ is a preorder. ⊆-preorder : ∀ {a} → Set a → Preorder _ _ _ ⊆-preorder A = Ind.InducedPreorder₂ (PropEq.setoid (List A)) _∈_ (PropEq.subst (_∈_ _)) -- Set and bag equality and related preorders. open Related public using (Kind; Symmetric-kind) renaming ( implication to subset ; reverse-implication to superset ; equivalence to set ; injection to subbag ; reverse-injection to superbag ; bijection to bag ) [_]-Order : Kind → ∀ {a} → Set a → Preorder _ _ _ [ k ]-Order A = Related.InducedPreorder₂ k (_∈_ {A = A}) [_]-Equality : Symmetric-kind → ∀ {a} → Set a → Setoid _ _ [ k ]-Equality A = Related.InducedEquivalence₂ k (_∈_ {A = A}) infix 4 _∼[_]_ _∼[_]_ : ∀ {a} {A : Set a} → List A → Kind → List A → Set _ _∼[_]_ {A = A} xs k ys = Preorder._∼_ ([ k ]-Order A) xs ys -- Bag equality implies the other relations. bag-=⇒ : ∀ {k a} {A : Set a} {xs ys : List A} → xs ∼[ bag ] ys → xs ∼[ k ] ys bag-=⇒ xs≈ys = ↔⇒ xs≈ys -- "Equational" reasoning for _⊆_. module ⊆-Reasoning where import Relation.Binary.PreorderReasoning as PreR private open module PR {a} {A : Set a} = PreR (⊆-preorder A) public renaming (_∼⟨_⟩_ to _⊆⟨_⟩_; _≈⟨_⟩_ to _≡⟨_⟩_) infixr 2 _∼⟨_⟩_ infix 1 _∈⟨_⟩_ _∈⟨_⟩_ : ∀ {a} {A : Set a} x {xs ys : List A} → x ∈ xs → xs IsRelatedTo ys → x ∈ ys x ∈⟨ x∈xs ⟩ xs⊆ys = (begin xs⊆ys) x∈xs _∼⟨_⟩_ : ∀ {k a} {A : Set a} xs {ys zs : List A} → xs ∼[ ⌊ k ⌋→ ] ys → ys IsRelatedTo zs → xs IsRelatedTo zs xs ∼⟨ xs≈ys ⟩ ys≈zs = xs ⊆⟨ ⇒→ xs≈ys ⟩ ys≈zs ------------------------------------------------------------------------ -- Another function -- If any element satisfies P, then P is satisfied. satisfied : ∀ {a p} {A : Set a} {P : A → Set p} {xs} → Any P xs → ∃ P satisfied = Prod.map id Prod.proj₂ ∘ Membership-≡.find