# Library LibTactics

A library of additional tactics.

Implementation note: We want string_scope to be available for
the Case tactics below, but we want "++" to denote list
concatenation.

Open Scope string_scope.

Open Scope list_scope.

unsimpl E replaces all occurences of X in the goal by E,
where X is the result that tactic simpl would give when used
to reduce E.

Tactic Notation "unsimpl" constr(E) :=

let F := (eval simpl in E) in change F with E.

fold any not folds all occurrences of not in the goal. It's
useful for "cleaning up" after the intuition tactic.

Tactic Notation "fold" "any" "not" :=

repeat (

match goal with

| H: context [?P -> False] |- _ =>

fold (~ P) in H

| |- context [?P -> False] =>

fold (~ P)

end).

The following tactics call (e)apply with the first hypothesis
that succeeds, "first" meaning the hypothesis that comes earliest
in the context, i.e., higher up in the list.

Ltac apply_first_hyp :=

match reverse goal with

| H : _ |- _ => apply H

end.

Ltac eapply_first_hyp :=

match reverse goal with

| H : _ |- _ => eapply H

end.

Tactic Notation "assert_eq" ident(x) constr(v) :=

let H := fresh in

assert (x = v) as H by reflexivity;

clear H.

Tactic Notation "Case_aux" ident(x) constr(name) :=

first [

set (x := name); move x at top

| assert_eq x name

| fail 1 "because we are working on a different case." ].

Ltac Case name := Case_aux case name.

Ltac SCase name := Case_aux subcase name.

Ltac SSCase name := Case_aux subsubcase name.

Ltac SSSCase name := Case_aux subsubsubcase name.

Ltac SSSSCase name := Case_aux subsubsubsubcase name.

## Example

One mode of use for the above tactics is to wrap Coq's induction tactic such that it automatically inserts "case" markers into each branch of the proof. For example:

Tactic Notation "induction" "nat" ident(n) := induction n; [ Case "O" | Case "S" ]. Tactic Notation "sub" "induction" "nat" ident(n) := induction n; [ SCase "O" | SCase "S" ]. Tactic Notation "sub" "sub" "induction" "nat" ident(n) := induction n; [ SSCase "O" | SSCase "S" ].

Within a proof, one might use the tactics as follows:

induction nat n. (* or [induction n] *) Case "O". ... Case "S". ...

If you use such customized versions of the induction tactics, then the Case tactic will verify that you are working on the case that you think you are. You may also use the Case tactic with the standard version of induction, in which case no verification is done.

In general, you may use the Case tactics anywhere in a proof you wish to leave a "comment marker" in the context.

ltac_map applies a function F, with return type T and
exactly one non-implicit argument, to everything in the context
such that the application type checks. The tactic returns a list
containing the results of the applications.

Implementation note: The check for duplicates in the accumulator (match acc with ...) is necessary to ensure that the tactic does not go into an infinite loop.

Implementation note: The check for duplicates in the accumulator (match acc with ...) is necessary to ensure that the tactic does not go into an infinite loop.

Ltac ltac_map F :=

let rec map acc :=

match goal with

| H : _ |- _ =>

let FH := constr:(F H) in

match acc with

| context [FH] => fail 1

| _ => map (List.cons FH acc)

end

| _ => acc

end

in

let rec ret T :=

match T with

| _ -> ?T' => ret T'

| ?T' => T'

end

in

let T := ret ltac:(type of F) in

let res := map (@List.nil T) in

eval simpl in res.

ltac_map_list tac xs applies tac to each element of xs,
where xs is a Coq list.

Ltac ltac_map_list tac xs :=

match xs with

| List.nil => idtac

| List.cons ?x ?xs => tac x; ltac_map_list tac xs

end.

ltac_remove_dups takes a list and removes duplicate items from
it. The supplied list must, after simplification via simpl, be
built from only nil and cons. Duplicates are recognized only
"up to syntax," i.e., the limitations of Ltac's context
check.

Ltac ltac_remove_dups xs :=

let rec remove xs acc :=

match xs with

| List.nil => acc

| List.cons ?x ?xs =>

match acc with

| context [x] => remove xs acc

| _ => remove xs (List.cons x acc)

end

end

in

match type of xs with

| List.list ?A =>

let xs := eval simpl in xs in

let xs := remove xs (@List.nil A) in

eval simpl in (List.rev xs)

end.

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