Library iris.proofmode.ident_name

From stdpp Require Import base.
From iris.prelude Require Import options.

ident_name is a way to remember an identifier within the binder of a (trivial) function, which can be constructed and retrieved with Ltac but is easy to forward around opaquely in Gallina (through typeclasses, for example)
Definition ident_name := unit unit.

to_ident_name id returns a constr of type ident_name that holds id in the binder name
Ltac to_ident_name id :=
  eval cbv in (ltac:(clear; intros id; assumption) : unit unit).

to_ident_name is a Gallina-level version of to_ident_name for constructing ident_name literals.
Notation to_ident_name id := (λ id:unit, id) (only parsing).

The idea of AsIdentName is to convert the binder in f, which should be a lambda, to an ident_name representing the name of the binder. It has only one instance, a Hint Extern which implements that conversion to resolve name in Ltac (see solve_as_ident_name).
This typeclass can produce the fallback identifier __unknown when applied to an identifier rather than a lambda; for example, if the user writes bi_exist Φ, there is no binder anywhere to extract.
Class AsIdentName {A B} (f : A B) (name : ident_name) := as_ident_name {}.
Global Arguments as_ident_name {A B f} name : assert.

Ltac solve_as_ident_name :=
  lazymatch goal with
  
  | |- AsIdentName (λ H, _) _
    let name := to_ident_name H in
    notypeclasses refine (as_ident_name name)
  | _notypeclasses refine (to_ident_name __unknown)
  end.

Global Hint Extern 1 (AsIdentName _ _) ⇒ solve_as_ident_name : typeclass_instances.