From d236c7362053c4fc8f1c7f3b59248b412b029fb8 Mon Sep 17 00:00:00 2001 From: Gaëtan Gilbert Date: Thu, 21 Jun 2018 18:02:40 +0200 Subject: Define and use UGraph.enforce_leq_alg for subtyping inference Not sure if worth using in other places. --- kernel/uGraph.ml | 39 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) (limited to 'kernel/uGraph.ml') diff --git a/kernel/uGraph.ml b/kernel/uGraph.ml index 4a9467de5..bc624ba56 100644 --- a/kernel/uGraph.ml +++ b/kernel/uGraph.ml @@ -747,6 +747,45 @@ let check_constraint g (l,d,r) = let check_constraints c g = Constraint.for_all (check_constraint g) c +let leq_expr (u,m) (v,n) = + let d = match m - n with + | 1 -> Lt + | diff -> assert (diff <= 0); Le + in + (u,d,v) + +let enforce_leq_alg u v g = + let enforce_one (u,v) = function + | Inr _ as orig -> orig + | Inl (cstrs,g) as orig -> + if check_smaller_expr g u v then orig + else + (let c = leq_expr u v in + match enforce_constraint c g with + | g -> Inl (Constraint.add c cstrs,g) + | exception (UniverseInconsistency _ as e) -> Inr e) + in + (* max(us) <= max(vs) <-> forall u in us, exists v in vs, u <= v *) + let c = Universe.map (fun u -> Universe.map (fun v -> (u,v)) v) u in + let c = List.cartesians enforce_one (Inl (Constraint.empty,g)) c in + (* We pick a best constraint: smallest number of constraints, not an error if possible. *) + let order x y = match x, y with + | Inr _, Inr _ -> 0 + | Inl _, Inr _ -> -1 + | Inr _, Inl _ -> 1 + | Inl (c,_), Inl (c',_) -> + Int.compare (Constraint.cardinal c) (Constraint.cardinal c') + in + match List.min order c with + | Inl x -> x + | Inr e -> raise e + +(* sanity check wrapper *) +let enforce_leq_alg u v g = + let _,g as cg = enforce_leq_alg u v g in + assert (check_leq g u v); + cg + (* Normalization *) (** [normalize_universes g] returns a graph where all edges point -- cgit v1.2.3