------------------------------------------------------------------------
-- The Agda standard library
--
-- Properties related to All
------------------------------------------------------------------------

module Data.List.All.Properties where

open import Data.Bool.Base using (Bool; T)
open import Data.Bool.Properties
open import Data.Empty
open import Data.Fin using (Fin) renaming (zero to fzero; suc to fsuc)
open import Data.List.Base
open import Data.List.Any.Membership.Propositional
open import Data.List.All as All using (All; []; _∷_)
open import Data.List.Any using (Any; here; there)
open import Data.Nat using (zero; suc; z≤n; s≤s; _<_)
open import Data.Product as Prod using (_×_; _,_; uncurry; uncurry′)
open import Function
open import Function.Equality using (_⟨$⟩_)
open import Function.Equivalence using (_⇔_; module Equivalence)
open import Function.Inverse using (_↔_)
open import Function.Surjection using (_↠_)
open import Relation.Binary.PropositionalEquality as P using (_≡_)
open import Relation.Nullary
open import Relation.Unary
  using (Decidable; Universal) renaming (_⊆_ to _⋐_)

------------------------------------------------------------------------
-- When P is universal All P holds

module _ {a p} {A : Set a} {P : A  Set p} where

  All-universal : Universal P   xs  All P xs
  All-universal u [] = []
  All-universal u (x  xs) = u x  All-universal u xs

------------------------------------------------------------------------
-- Lemmas relating Any, All and negation.

module _ {a p} {A : Set a} {P : A  Set p} where

  ¬Any⇒All¬ :  xs  ¬ Any P xs  All (¬_  P) xs
  ¬Any⇒All¬ []       ¬p = []
  ¬Any⇒All¬ (x  xs) ¬p = ¬p  here  ¬Any⇒All¬ xs (¬p  there)

  All¬⇒¬Any :  {xs}  All (¬_  P) xs  ¬ Any P xs
  All¬⇒¬Any []        ()
  All¬⇒¬Any (¬p  _)  (here  p) = ¬p p
  All¬⇒¬Any (_   ¬p) (there p) = All¬⇒¬Any ¬p p

  ¬All⇒Any¬ : Decidable P   xs  ¬ All P xs  Any (¬_  P) xs
  ¬All⇒Any¬ dec []       ¬∀ = ⊥-elim (¬∀ [])
  ¬All⇒Any¬ dec (x  xs) ¬∀ with dec x
  ... | yes p = there (¬All⇒Any¬ dec xs (¬∀  _∷_ p))
  ... | no ¬p = here ¬p

  Any¬→¬All :  {xs}  Any (¬_  P) xs  ¬ All P xs
  Any¬→¬All (here  ¬p) = ¬p            All.head
  Any¬→¬All (there ¬p) = Any¬→¬All ¬p  All.tail

  ¬Any↠All¬ :  {xs}  (¬ Any P xs)  All (¬_  P) xs
  ¬Any↠All¬ = record
    { to         = P.→-to-⟶ (¬Any⇒All¬ _)
    ; surjective = record
      { from             = P.→-to-⟶ All¬⇒¬Any
      ; right-inverse-of = to∘from
      }
    }
    where

    to∘from :  {xs} (¬p : All (¬_  P) xs)  ¬Any⇒All¬ xs (All¬⇒¬Any ¬p)  ¬p
    to∘from []         = P.refl
    to∘from (¬p  ¬ps) = P.cong₂ _∷_ P.refl (to∘from ¬ps)

    -- If equality of functions were extensional, then the surjection
    -- could be strengthened to a bijection.

    from∘to : P.Extensionality _ _ 
               xs  (¬p : ¬ Any P xs)  All¬⇒¬Any (¬Any⇒All¬ xs ¬p)  ¬p
    from∘to ext []       ¬p = ext λ ()
    from∘to ext (x  xs) ¬p = ext λ
      { (here p)   P.refl
      ; (there p)  P.cong  f  f p) $ from∘to ext xs (¬p  there)
      }

  Any¬⇔¬All :  {xs}  Decidable P  Any (¬_  P) xs  (¬ All P xs)
  Any¬⇔¬All dec = record
    { to   = P.→-to-⟶ Any¬→¬All
    ; from = P.→-to-⟶ (¬All⇒Any¬ dec _)
    }
    where

    -- If equality of functions were extensional, then the logical
    -- equivalence could be strengthened to a surjection.

    to∘from : P.Extensionality _ _ 
               {xs} (¬∀ : ¬ All P xs)  Any¬→¬All (¬All⇒Any¬ dec xs ¬∀)  ¬∀
    to∘from ext ¬∀ = ext (⊥-elim  ¬∀)

------------------------------------------------------------------------
-- Lemmas relating All to ⊤

All-all :  {a} {A : Set a} (p : A  Bool) {xs} 
          All (T  p) xs  T (all p xs)
All-all p []         = _
All-all p (px  pxs) = Equivalence.from T-∧ ⟨$⟩ (px , All-all p pxs)

all-All :  {a} {A : Set a} (p : A  Bool) xs 
          T (all p xs)  All (T  p) xs
all-All p []       _     = []
all-All p (x  xs) px∷xs with Equivalence.to (T-∧ {p x}) ⟨$⟩ px∷xs
all-All p (x  xs) px∷xs | (px , pxs) = px  all-All p xs pxs

------------------------------------------------------------------------
-- All is anti-monotone.

anti-mono :  {a p} {A : Set a} {P : A  Set p} {xs ys} 
            xs  ys  All P ys  All P xs
anti-mono xs⊆ys pys = All.tabulate (All.lookup pys  xs⊆ys)

all-anti-mono :  {a} {A : Set a} (p : A  Bool) {xs ys} 
                xs  ys  T (all p ys)  T (all p xs)
all-anti-mono p xs⊆ys = All-all p  anti-mono xs⊆ys  all-All p _

------------------------------------------------------------------------
-- Introduction (⁺) and elimination (⁻) rules for various list functions
------------------------------------------------------------------------
-- map

module _{a b} {A : Set a} {B : Set b} where

  All-map :  {p} {P : B  Set p} {f : A  B} {xs} 
            All (P  f) xs  All P (map f xs)
  All-map []       = []
  All-map (p  ps) = p  All-map ps

  map-All :  {p} {P : B  Set p} {f : A  B} {xs} 
            All P (map f xs)  All (P  f) xs
  map-All {xs = []}    []       = []
  map-All {xs = _  _} (p  ps) = p  map-All ps

  -- A variant of All.map.

  gmap :  {p q} {P : A  Set p} {Q : B  Set q} {f : A  B} 
         P  Q  f  All P  All Q  map f
  gmap g = All-map  All.map g

------------------------------------------------------------------------
-- _++_

module _ {a p} {A : Set a} {P : A  Set p} where

  ++⁺ :  {xs ys}  All P xs  All P ys  All P (xs ++ ys)
  ++⁺ []         pys = pys
  ++⁺ (px  pxs) pys = px  ++⁺ pxs pys

  ++⁻ˡ :  xs {ys}  All P (xs ++ ys)  All P xs
  ++⁻ˡ []       p          = []
  ++⁻ˡ (x  xs) (px  pxs) = px  (++⁻ˡ _ pxs)

  ++⁻ʳ :  xs {ys}  All P (xs ++ ys)  All P ys
  ++⁻ʳ []       p          = p
  ++⁻ʳ (x  xs) (px  pxs) = ++⁻ʳ xs pxs

  ++⁻ :  xs {ys}  All P (xs ++ ys)  All P xs × All P ys
  ++⁻ []       p          = [] , p
  ++⁻ (x  xs) (px  pxs) = Prod.map (px ∷_) id (++⁻ _ pxs)

  ++↔ :  {xs ys}  (All P xs × All P ys)  All P (xs ++ ys)
  ++↔ {xs} = record
    { to         = P.→-to-⟶ $ uncurry ++⁺
    ; from       = P.→-to-⟶ $ ++⁻ xs
    ; inverse-of = record
      { left-inverse-of  = ++⁻∘++⁺
      ; right-inverse-of = ++⁺∘++⁻ xs
      }
    }
    where

    ++⁺∘++⁻ :  xs {ys} (p : All P (xs ++ ys)) 
              uncurry′ ++⁺ (++⁻ xs p)  p
    ++⁺∘++⁻ []       p          = P.refl
    ++⁺∘++⁻ (x  xs) (px  pxs) = P.cong (_∷_ px) $ ++⁺∘++⁻ xs pxs

    ++⁻∘++⁺ :  {xs ys} (p : All P xs × All P ys) 
              ++⁻ xs (uncurry ++⁺ p)  p
    ++⁻∘++⁺ ([]       , pys) = P.refl
    ++⁻∘++⁺ (px  pxs , pys) rewrite ++⁻∘++⁺ (pxs , pys) = P.refl

------------------------------------------------------------------------
-- concat

module _ {a p} {A : Set a} {P : A  Set p} where

  concat⁺ :  {xss}  All (All P) xss  All P (concat xss)
  concat⁺ []           = []
  concat⁺ (pxs  pxss) = ++⁺ pxs (concat⁺ pxss)

  concat⁻ :  {xss}  All P (concat xss)  All (All P) xss
  concat⁻ {[]}       []  = []
  concat⁻ {xs  xss} pxs = ++⁻ˡ xs pxs  concat⁻ (++⁻ʳ xs pxs)

------------------------------------------------------------------------
-- take and drop

module _ {a p} {A : Set a} {P : A  Set p} where

  drop⁺ :  {xs} n  All P xs  All P (drop n xs)
  drop⁺ zero    pxs        = pxs
  drop⁺ (suc n) []         = []
  drop⁺ (suc n) (px  pxs) = drop⁺ n pxs

  take⁺ :  {xs} n  All P xs  All P (take n xs)
  take⁺ zero    pxs        = []
  take⁺ (suc n) []         = []
  take⁺ (suc n) (px  pxs) = px  take⁺ n pxs

------------------------------------------------------------------------
-- applyUpTo

module _ {a p} {A : Set a} {P : A  Set p} where

  applyUpTo⁺₁ :  f n  (∀ {i}  i < n  P (f i))  All P (applyUpTo f n)
  applyUpTo⁺₁ f zero    Pf = []
  applyUpTo⁺₁ f (suc n) Pf = Pf (s≤s z≤n)  applyUpTo⁺₁ (f  suc) n (Pf  s≤s)

  applyUpTo⁺₂ :  f n  (∀ i  P (f i))  All P (applyUpTo f n)
  applyUpTo⁺₂ f n Pf = applyUpTo⁺₁ f n  _  Pf _)

  applyUpTo⁻ :  f n  All P (applyUpTo f n)   {i}  i < n  P (f i)
  applyUpTo⁻ f zero    pxs        ()
  applyUpTo⁻ f (suc n) (px  _)   (s≤s z≤n)       = px
  applyUpTo⁻ f (suc n) (_   pxs) (s≤s (s≤s i<n)) =
    applyUpTo⁻ (f  suc) n pxs (s≤s i<n)

------------------------------------------------------------------------
-- tabulate

module _ {a p} {A : Set a} {P : A  Set p} where

  tabulate⁺ :  {n} {f : Fin n  A} 
              (∀ i  P (f i))  All P (tabulate f)
  tabulate⁺ {zero}  Pf = []
  tabulate⁺ {suc n} Pf = Pf fzero  tabulate⁺ (Pf  fsuc)

  tabulate⁻ :  {n} {f : Fin n  A} 
              All P (tabulate f)  (∀ i  P (f i))
  tabulate⁻ {zero}  pf       ()
  tabulate⁻ {suc n} (px  _) fzero    = px
  tabulate⁻ {suc n} (_  pf) (fsuc i) = tabulate⁻ pf i