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------------------------------------------------------------------------
-- The Agda standard library
--
-- Membership of vectors, along with some additional definitions.
------------------------------------------------------------------------

{-# OPTIONS --cubical-compatible --safe #-}

open import Relation.Binary using (Setoid; _Respects_)

module Data.Vec.Membership.Setoid {c } (S : Setoid c ) where

open import Function
open import Data.Vec.Base as Vec using (Vec; []; _∷_)
open import Data.Vec.Relation.Unary.Any as Any
  using (Any; here; there; index)
open import Data.Product using (; _×_; _,_)
open import Relation.Nullary using (¬_)
open import Relation.Unary using (Pred)

open Setoid S renaming (Carrier to A)

------------------------------------------------------------------------
-- Definitions

infix 4 _∈_ _∉_

_∈_ : A   {n}  Vec A n  Set _
x  xs = Any (x ≈_) xs

_∉_ : A   {n}  Vec A n  Set _
x  xs = ¬ x  xs

------------------------------------------------------------------------
-- Operations

mapWith∈ :  {b} {B : Set b} {n}
           (xs : Vec A n)  (∀ {x}  x  xs  B)  Vec B n
mapWith∈ []       f = []
mapWith∈ (x  xs) f = f (here refl)  mapWith∈ xs (f  there)

_∷=_ :  {n} {xs : Vec A n} {x}  x  xs  A  Vec A n
_∷=_ {xs = xs} x∈xs v = xs Vec.[ index x∈xs ]≔ v

------------------------------------------------------------------------
-- Finding and losing witnesses

module _ {p} {P : Pred A p} where

  find :  {n} {xs : Vec A n}  Any P xs   λ x  x  xs × P x
  find (here px)   = (_ , here refl , px)
  find (there pxs) with find pxs
  ... | (x , x∈xs , px) = (x , there x∈xs , px)

  lose : P Respects _≈_   {x n} {xs : Vec A n}  x  xs  P x  Any P xs
  lose resp x∈xs px = Any.map (flip resp px) x∈xs