✨ Directed relation option->list

examples/list_option.v

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+(*****************************************************************************)
+(*                            *                    Trocq                     *)
+(*  _______                   *       Copyright (C) 2023 Inria & MERCE       *)
+(* |__   __|                  *    (Mitsubishi Electric R&D Centre Europe)   *)
+(*    | |_ __ ___   ___ __ _  *       Cyril Cohen <[email protected]>     *)
+(*    | | '__/ _ \ / __/ _` | *       Enzo Crance <[email protected]>     *)
+(*    | | | | (_) | (_| (_| | *   Assia Mahboubi <[email protected]>   *)
+(*    |_|_|  \___/ \___\__, | ************************************************)
+(*                        | | * This file is distributed under the terms of  *)
+(*                        |_| * GNU Lesser General Public License Version 3  *)
+(*                            * see LICENSE file for the text of the license *)
+(*****************************************************************************)
+
+From Coq Require Import ssreflect.
+From Trocq Require Import Trocq.
+From Trocq Require Import Param_trans Param_list.
+
+Definition option_to_list {A : Type} (xo : option A) : list A :=
+  match xo with
+  | None => nil
+  | Some x => cons x nil
+  end.
+
+Definition list_to_option {A : Type} (l : list A) : option A :=
+  match l with
+  | nil => None
+  | cons x _ => Some x
+  end.
+
+Theorem option_to_listR (A : Type) (xo : option A) : list_to_option (option_to_list xo) = xo.
+Proof. destruct xo; reflexivity. Qed.
+
+Definition option_list_inj (A : Type) : @SplitInj.type (option A) (list A) :=
+  SplitInj.Build (option_to_listR A).
+
+Definition Param_option_list_d (A : Type) : Param42b.Rel (option A) (list A) :=
+  SplitInj.toParam (option_list_inj A).
+
+Definition Param42b_option_list (A A' : Type) (AR : Param42b.Rel A A') :
+  Param42b.Rel (option A) (list A').
+Proof.
+  apply (@Param42b_trans _ (list A)).
+  - apply Param_option_list_d.
+  - apply (Param42b_list A A' AR).
+Defined.
+Trocq Use Param42b_option_list.
+
+Definition omap {A B : Type} (f : A -> B) (xo : option A) : option B :=
+  match xo with
+  | None => None
+  | Some x => Some (f x)
+  end.
+
+Definition map {A B : Type} (f : A -> B) : list A -> list B :=
+  fix F l :=
+    match l with
+    | nil => nil
+    | cons a l => cons (f a) (F l)
+    end.
+
+Definition mapR
+  (A A' : Type) (AR : Param00.Rel A A')
+  (B B' : Type) (BR : Param00.Rel B B')
+  (f : A -> B) (f' : A' -> B') (fR : R_arrow AR BR f f')
+  (l : list A) (l' : list A') (lR : listR A A' AR l l') :
+    listR B B' BR (map f l) (map f' l').
+Proof.
+  induction lR; simpl.
+  - apply nilR.
+  - apply consR.
+    + apply (fR a a' aR).
+    + apply IHlR.
+Defined.
+
+Lemma option_to_list_map_morph (A B : Type) (f : A -> B) (xo : option A) :
+  option_to_list (omap f xo) = map f (option_to_list xo).
+Proof. destruct xo; reflexivity. Qed.
+
+Definition omap_map_R
+  (A A' : Type) (AR : Param42b.Rel A A')
+  (B B' : Type) (BR : Param42b.Rel B B')
+  (f : A -> B) (f' : A' -> B') (fR : R_arrow AR BR f f')
+  (xo : option A) (l' : list A') (r : Param42b_option_list A A' AR xo l') :
+    Param42b_option_list B B' BR (omap f xo) (map f' l').
+Proof.
+  destruct r as [l [r lR]].
+  unshelve econstructor.
+  - exact (map f l).
+  - split.
+    + rewrite <- r. apply option_to_list_map_morph.
+    + exact (mapR A A' AR B B' BR f f' fR l l' lR).
+Defined.
+Trocq Use omap_map_R.
+
+Trocq Use Param01_paths.
+
+Theorem map_compose (A B C : Type) (l : list A) (f : A -> B) (g : B -> C) :
+  map g (map f l) = map (fun x => g (f x)) l.
+Proof.
+  induction l; simpl.
+  - reflexivity.
+  - apply ap. apply IHl.
+Qed.
+
+Goal forall A B C (xo : option A) (f : A -> B) (g : B -> C),
+  omap g (omap f xo) = omap (fun x => g (f x)) xo.
+Proof.
+  trocq. apply map_compose.
+Qed.