------------------------------------------------------------------------ -- The Agda standard library -- -- Lists where at least one element satisfies a given property ------------------------------------------------------------------------ {-# OPTIONS --without-K --safe #-} module Data.List.Relation.Unary.Any where open import Data.Empty open import Data.Fin.Base open import Data.List.Base as List using (List; []; [_]; _∷_) open import Data.Product as Prod using (∃; _,_) open import Data.Sum.Base as Sum using (_⊎_; inj₁; inj₂) open import Level using (Level; _⊔_) open import Relation.Nullary using (¬_; yes; no) import Relation.Nullary.Decidable as Dec open import Relation.Nullary.Negation using (contradiction) open import Relation.Nullary.Sum using (_⊎-dec_) open import Relation.Unary hiding (_∈_) private variable a p q : Level A : Set a P Q : Pred A p x : A xs : List A ------------------------------------------------------------------------ -- Definition -- Given a predicate P, then Any P xs means that at least one element -- in xs satisfies P. See `Relation.Unary` for an explanation of -- predicates. data Any {A : Set a} (P : Pred A p) : Pred (List A) (a ⊔ p) where here : ∀ {x xs} (px : P x) → Any P (x ∷ xs) there : ∀ {x xs} (pxs : Any P xs) → Any P (x ∷ xs) ------------------------------------------------------------------------ -- Operations on Any head : ¬ Any P xs → Any P (x ∷ xs) → P x head ¬pxs (here px) = px head ¬pxs (there pxs) = contradiction pxs ¬pxs tail : ¬ P x → Any P (x ∷ xs) → Any P xs tail ¬px (here px) = ⊥-elim (¬px px) tail ¬px (there pxs) = pxs map : P ⊆ Q → Any P ⊆ Any Q map g (here px) = here (g px) map g (there pxs) = there (map g pxs) -- `index x∈xs` is the list position (zero-based) which `x∈xs` points to. index : Any P xs → Fin (List.length xs) index (here px) = zero index (there pxs) = suc (index pxs) lookup : {P : Pred A p} → Any P xs → A lookup {xs = xs} p = List.lookup xs (index p) _∷=_ : {P : Pred A p} → Any P xs → A → List A _∷=_ {xs = xs} x∈xs v = xs List.[ index x∈xs ]∷= v infixl 4 _─_ _─_ : {P : Pred A p} → ∀ xs → Any P xs → List A xs ─ x∈xs = xs List.─ index x∈xs -- If any element satisfies P, then P is satisfied. satisfied : Any P xs → ∃ P satisfied (here px) = _ , px satisfied (there pxs) = satisfied pxs toSum : Any P (x ∷ xs) → P x ⊎ Any P xs toSum (here px) = inj₁ px toSum (there pxs) = inj₂ pxs fromSum : P x ⊎ Any P xs → Any P (x ∷ xs) fromSum (inj₁ px) = here px fromSum (inj₂ pxs) = there pxs ------------------------------------------------------------------------ -- Properties of predicates preserved by Any any? : Decidable P → Decidable (Any P) any? P? [] = no λ() any? P? (x ∷ xs) = Dec.map′ fromSum toSum (P? x ⊎-dec any? P? xs) satisfiable : Satisfiable P → Satisfiable (Any P) satisfiable (x , Px) = [ x ] , here Px ------------------------------------------------------------------------ -- DEPRECATED ------------------------------------------------------------------------ -- Please use the new names as continuing support for the old names is -- not guaranteed. -- Version 1.4 any = any? {-# WARNING_ON_USAGE any "Warning: any was deprecated in v1.4. Please use any? instead." #-}