------------------------------------------------------------------------
-- The Agda standard library
--
-- All predicate transformer for fresh lists
------------------------------------------------------------------------

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

module Data.List.Fresh.Relation.Unary.All where

open import Level using (Level; _⊔_; Lift)
open import Data.Product.Base using (_×_; _,_; proj₁; uncurry)
open import Data.Sum.Base as Sum using (inj₁; inj₂)
open import Relation.Nullary.Decidable as Dec using (Dec; yes; no; _×-dec_)
open import Relation.Unary  as U
open import Relation.Binary.Core using (Rel)

open import Data.List.Fresh using (List#; []; cons; _∷#_; _#_)
open import Data.List.Fresh.Relation.Unary.Any as Any using (Any; here; there)

private
  variable
    a p q r : Level
    A : Set a

module _ {A : Set a} {R : Rel A r} (P : Pred A p) where

  infixr 5 _∷_

  data All : List# A R  Set (p  a  r) where
    []  : All []
    _∷_ :  {x xs pr}  P x  All xs  All (cons x xs pr)

module _ {R : Rel A r} {P : Pred A p} where

  uncons :  {x} {xs : List# A R} {pr} 
           All P (cons x xs pr)  P x × All P xs
  uncons (p  ps) = p , ps

module _ {R : Rel A r} where

  append   : (xs ys : List# A R)  All (_# ys) xs  List# A R
  append-# :  {x} xs ys {ps}  x # xs  x # ys  x # append xs ys ps

  append []             ys _  = ys
  append (cons x xs pr) ys ps =
    let (p , ps) = uncons ps in
    cons x (append xs ys ps) (append-# xs ys pr p)

  append-# []             ys x#xs       x#ys = x#ys
  append-# (cons x xs pr) ys (r , x#xs) x#ys = r , append-# xs ys x#xs x#ys

module _ {R : Rel A r} {P : Pred A p} {Q : Pred A q} where

  map :  {xs : List# A R}  ∀[ P  Q ]  All P xs  All Q xs
  map p⇒q []       = []
  map p⇒q (p  ps) = p⇒q p  map p⇒q ps

  lookup :  {xs : List# A R}  All Q xs  (ps : Any P xs) 
           Q (proj₁ (Any.witness ps))
  lookup (q  _)  (here _)  = q
  lookup (_  qs) (there k) = lookup qs k

module _ {R : Rel A r} {P : Pred A p} (P? : Decidable P) where

  all? : (xs : List# A R)  Dec (All P xs)
  all? []        = yes []
  all? (x ∷# xs) = Dec.map′ (uncurry _∷_) uncons (P? x ×-dec all? xs)

------------------------------------------------------------------------
-- Generalised decidability procedure

module _ {R : Rel A r} {P : Pred A p} {Q : Pred A q} where

  decide :  Π[ P  Q ]  Π[ All {R = R} P  Any Q ]
  decide p∪q [] = inj₁ []
  decide p∪q (x ∷# xs) with p∪q x
  ... | inj₂ qx = inj₂ (here qx)
  ... | inj₁ px = Sum.map (px ∷_) there (decide p∪q xs)