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

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

module Data.Vec.Relation.Unary.AllPairs.Properties where

open import Data.Vec.Base using (_∷_; map; _++_; concat; take; drop; tabulate)
import Data.Vec.Properties as Vec
open import Data.Vec.Relation.Unary.All as All using (All; []; _∷_)
import Data.Vec.Relation.Unary.All.Properties as All
open import Data.Vec.Relation.Unary.AllPairs as AllPairs using (AllPairs; []; _∷_)
open import Data.Bool.Base using (true; false)
open import Data.Fin.Base using (Fin)
open import Data.Fin.Properties using (suc-injective)
open import Data.Nat.Base using (zero; suc; _+_)
open import Function.Base using (_∘_)
open import Level using (Level)
open import Relation.Binary.Core using (Rel)
open import Relation.Binary.PropositionalEquality.Core using (_≢_)

private
  variable
    a b c p  : Level
    A : Set a
    B : Set b
    C : Set c

------------------------------------------------------------------------
-- Introduction (⁺) and elimination (⁻) rules for vector operations
------------------------------------------------------------------------
-- map

module _ {R : Rel A } {f : B  A} where

  map⁺ :  {n xs}  AllPairs  x y  R (f x) (f y)) {n} xs 
         AllPairs R {n} (map f xs)
  map⁺ []           = []
  map⁺ (x∉xs  xs!) = All.map⁺ x∉xs  map⁺ xs!

------------------------------------------------------------------------
-- ++

module _ {R : Rel A } where

  ++⁺ :  {n m xs ys}  AllPairs R {n} xs  AllPairs R {m} ys 
        All  x  All (R x) ys) xs  AllPairs R (xs ++ ys)
  ++⁺ []         Rys _              = Rys
  ++⁺ (px  Rxs) Rys (Rxys  Rxsys) = All.++⁺ px Rxys  ++⁺ Rxs Rys Rxsys

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

module _ {R : Rel A } where

  concat⁺ :  {n m xss}  All (AllPairs R {n}) {m} xss 
            AllPairs  xs ys  All  x  All (R x) ys) xs) xss 
            AllPairs R (concat xss)
  concat⁺ []           []              = []
  concat⁺ (pxs  pxss) (Rxsxss  Rxss) = ++⁺ pxs (concat⁺ pxss Rxss)
    (All.map All.concat⁺ (All.All-swap Rxsxss))

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

module _ {R : Rel A } where

  take⁺ :  {n} m {xs}  AllPairs R {m + n} xs  AllPairs R {m} (take m xs)
  take⁺ zero pxs = []
  take⁺ (suc m) {x  xs} (px  pxs) = All.take⁺ m px  take⁺ m pxs

  drop⁺ :  {n} m {xs}  AllPairs R {m + n} xs  AllPairs R {n} (drop m xs)
  drop⁺ zero pxs = pxs
  drop⁺ (suc m) (_  pxs) = drop⁺ m pxs

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

module _ {R : Rel A } where

  tabulate⁺ :  {n} {f : Fin n  A}  (∀ {i j}  i  j  R (f i) (f j)) 
              AllPairs R (tabulate f)
  tabulate⁺ {zero}  fᵢ~fⱼ = []
  tabulate⁺ {suc n} fᵢ~fⱼ =
    All.tabulate⁺  j  fᵢ~fⱼ λ()) 
    tabulate⁺ (fᵢ~fⱼ  (_∘ suc-injective))