### Document list_remove and list_remove_list.

parent 0a35ba52
Pipeline #3570 passed with stage
in 10 minutes and 54 seconds
 ... ... @@ -285,18 +285,20 @@ Inductive contains {A} : relation (list A) := Infix "`contains`" := contains (at level 70) : C_scope. Hint Extern 0 (_ `contains` _) => reflexivity. Section contains_dec_help. Context `{EqDecision A}. Fixpoint list_remove (x : A) (l : list A) : option (list A) := match l with | [] => None | y :: l => if decide (x = y) then Some l else (y ::) <\$> list_remove x l end. Fixpoint list_remove_list (k : list A) (l : list A) : option (list A) := match k with | [] => Some l | x :: k => list_remove x l ≫= list_remove_list k end. End contains_dec_help. (** Removes [x] from the list [l]. The function returns a [Some] when the +removal succeeds and [None] when [x] is not in [l]. *) Fixpoint list_remove `{EqDecision A} (x : A) (l : list A) : option (list A) := match l with | [] => None | y :: l => if decide (x = y) then Some l else (y ::) <\$> list_remove x l end. (** Removes all elements in the list [k] from the list [l]. The function returns a [Some] when the removal succeeds and [None] some element of [k] is not in [l]. *) Fixpoint list_remove_list `{EqDecision A} (k : list A) (l : list A) : option (list A) := match k with | [] => Some l | x :: k => list_remove x l ≫= list_remove_list k end. Inductive Forall3 {A B C} (P : A → B → C → Prop) : list A → list B → list C → Prop := ... ...
• Owner

Wow, these are strange functions... why would they even be partial? My expectation would have been for `list_remove` to leave the list unchanged if `x` is not in there.

• Maintainer

Well, they were there, and while reading the code I decided to document them ;)

• Maintainer

It seems that they are mostly used to prove that contains is decidable. The key lemma for that is:

``l1 `contains` l2 ↔ is_Some (list_remove_list l1 l2).``
Markdown is supported
0% or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!