module U = FoUtils.Utils(B)
let unification vars locked_vars t1 t2 =
- let lookup = Subst.lookup_subst in
let rec occurs_check subst what where =
match where with
| Terms.Var i when i = what -> true
| Terms.Var i ->
- let t = lookup i subst in
+ let t = Subst.lookup i subst in
if not (U.eq_foterm t where) then occurs_check subst what t else false
| Terms.Node l -> List.exists (occurs_check subst what) l
| _ -> false
in
let rec unif subst s t =
- let s = match s with Terms.Var i -> lookup i subst | _ -> s
- and t = match t with Terms.Var i -> lookup i subst | _ -> t
+ let s = match s with Terms.Var i -> Subst.lookup i subst | _ -> s
+ and t = match t with Terms.Var i -> Subst.lookup i subst | _ -> t
in
match s, t with
let subst = unif Subst.id_subst t1 t2 in
let vars = Subst.filter subst vars in
subst, vars
-
+;;
+
+ let alpha_eq s t =
+ let rec equiv subst s t =
+ let s = match s with Terms.Var i -> Subst.lookup i subst | _ -> s
+ and t = match t with Terms.Var i -> Subst.lookup i subst | _ -> t
+
+ in
+ match s, t with
+ | s, t when U.eq_foterm s t -> subst
+ | Terms.Var i, Terms.Var j
+ when (not (List.exists (fun (_,k) -> k=t) subst)) ->
+ let subst = Subst.build_subst i t subst in
+ subst
+ | Terms.Node l1, Terms.Node l2 -> (
+ try
+ List.fold_left2
+ (fun subst' s t -> equiv subst' s t)
+ subst l1 l2
+ with Invalid_argument _ ->
+ raise (UnificationFailure (lazy "Inference.unification.unif"))
+ )
+ | _, _ ->
+ raise (UnificationFailure (lazy "Inference.unification.unif"))
+ in
+ equiv Subst.id_subst s t
+;;
+
end