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Class A := { foo : nat }.
Instance A_1 : A | 2 := { foo := 42 }.
Instance A_0 : A | 1 := { foo := 0 }.
Lemma aeq (a : A) : foo = foo.
reflexivity.
Qed.
Goal exists n, n = 42.
eexists.
eapply eq_trans.
evar (a : A). subst a.
refine (@aeq ?a).
Unshelve. all:cycle 1.
typeclasses eauto.
Fail reflexivity.
Undo 2.
Set Typeclasses Debug.
(* Without multiple successes it fails *)
Fail all:((once typeclasses eauto) + reflexivity).
(* Does backtrack if other goals fail *)
all:((typeclasses eauto) + reflexivity).
Qed.
Hint Extern 0 (_ = _) => reflexivity : typeclass_instances.
Goal exists n, n = 42.
eexists.
eapply eq_trans.
evar (a : A). subst a.
refine (@aeq ?a).
Unshelve. all:cycle 1.
typeclasses eauto.
Fail reflexivity.
Undo 2.
Set Typeclasses Debug.
(* Does backtrack between individual goals *)
all:(typeclasses eauto).
Qed.
Fail Timeout 1 Check prf.
Hint Mode SomeProp + + : typeclass_instances.
Check prf.
Check (fun H : SomeProp plus => _ : SomeProp (flip plus)).
(** Iterative deepening / breadth-first search *)
Module IterativeDeepening.
Class A.
Class B.
Class C.
Instance: B -> A | 0.
Instance: C -> A | 0.
Instance: C -> B -> A | 0.
Instance: A -> A | 0.
Goal C -> A.
intros.
Set Typeclasses Debug.
Fail Timeout 1 typeclasses eauto.
Set Typeclasses Iterative Deepening.
Fail typeclasses eauto 1.
typeclasses eauto 2.
Undo.
Unset Typeclasses Iterative Deepening.
Fail Timeout 1 typeclasses eauto.
Set Typeclasses Iterative Deepening.
Typeclasses eauto := debug 3.
typeclasses eauto.
Qed.
End IterativeDeepening.
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