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-rw-r--r--src/Util/Option.v62
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diff --git a/src/Util/Option.v b/src/Util/Option.v
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+Require Import Coq.Classes.Morphisms.
+
+Global Instance option_rect_Proper_nd {A T}
+ : Proper ((pointwise_relation _ eq) ==> eq ==> eq ==> eq) (@option_rect A (fun _ => T)).
+Proof.
+ intros ?? H ??? [|]??; subst; simpl; congruence.
+Qed.
+
+Global Instance option_rect_Proper_nd' {A T}
+ : Proper ((pointwise_relation _ eq) ==> eq ==> forall_relation (fun _ => eq)) (@option_rect A (fun _ => T)).
+Proof.
+ intros ?? H ??? [|]; subst; simpl; congruence.
+Qed.
+
+Hint Extern 1 (Proper _ (@option_rect ?A (fun _ => ?T))) => exact (@option_rect_Proper_nd' A T) : typeclass_instances.
+
+Lemma option_rect_option_map : forall {A B C} (f:A->B) some none v,
+ option_rect (fun _ => C) (fun x => some (f x)) none v = option_rect (fun _ => C) some none (option_map f v).
+Proof.
+ destruct v; reflexivity.
+Qed.
+
+Lemma option_rect_function {A B C S' N' v} f
+ : f (option_rect (fun _ : option A => option B) S' N' v)
+ = option_rect (fun _ : option A => C) (fun x => f (S' x)) (f N') v.
+Proof. destruct v; reflexivity. Qed.
+
+(*
+Ltac commute_option_rect_Let_In := (* pull let binders out side of option_rect pattern matching *)
+ idtac;
+ lazymatch goal with
+ | [ |- ?LHS = option_rect ?P ?S ?N (Let_In ?x ?f) ]
+ => (* we want to just do a [change] here, but unification is stupid, so we have to tell it what to unfold in what order *)
+ cut (LHS = Let_In x (fun y => option_rect P S N (f y))); cbv beta;
+ [ set_evars;
+ let H := fresh in
+ intro H;
+ rewrite H;
+ clear;
+ abstract (cbv [Let_In]; reflexivity)
+ | ]
+ end.
+*)
+
+(** TODO: possibly move me, remove local *)
+Ltac replace_option_match_with_option_rect :=
+ idtac;
+ lazymatch goal with
+ | [ |- _ = ?RHS :> ?T ]
+ => lazymatch RHS with
+ | match ?a with None => ?N | Some x => @?S x end
+ => replace RHS with (option_rect (fun _ => T) S N a) by (destruct a; reflexivity)
+ end
+ end.
+
+Ltac simpl_option_rect := (* deal with [option_rect _ _ _ None] and [option_rect _ _ _ (Some _)] *)
+ repeat match goal with
+ | [ |- context[option_rect ?P ?S ?N None] ]
+ => change (option_rect P S N None) with N
+ | [ |- context[option_rect ?P ?S ?N (Some ?x) ] ]
+ => change (option_rect P S N (Some x)) with (S x); cbv beta
+ end.