diff --git a/theories/base.v b/theories/base.v index 4dcc5852a52d0efdc6c17ca691d890f33b803260..12e6afd7e9a8018d52d4f16d766d7b9656da106e 100644 --- a/theories/base.v +++ b/theories/base.v @@ -62,6 +62,20 @@ of this type class. *) Class NoBackTrack (P : Prop) := { no_backtrack : P }. Hint Extern 0 (NoBackTrack _) => constructor; apply _ : typeclass_instances. +(* A conditional at the type class level. Note that [TCIf P Q R] is not the same +as [TCOr (TCAnd P Q) R]: the latter will backtrack to [R] if it fails to +establish [R], i.e. does not have the behavior of a conditional. Furthermore, +note that [TCOr (TCAnd P Q) (TCAnd (TCNot P) R)] would not work; we generally +would not be able to proof the negation of [P]. *) +Inductive TCIf (P Q R : Prop) := + | TCIf_true : P → Q → TCIf P Q R + | TCIf_false : R → TCIf P Q R. +Existing Class TCIf. + +Hint Extern 0 (TCIf _ _ _) => + first [apply TCIf_true; [apply _|] + |apply TCIf_false] : typeclass_instances. + (** * Typeclass opaque definitions *) (** The constant [tc_opaque] is used to make definitions opaque for just type class search. Note that [simpl] is set up to always unfold [tc_opaque]. *)