From b798b700f908d94c8ecd65783088f6925b8b3fe2 Mon Sep 17 00:00:00 2001 From: Stefano Zacchiroli Date: Thu, 22 Jan 2004 10:31:33 +0000 Subject: [PATCH] - splitted into cicMetaSubst - bugfixes - better exceptions --- helm/ocaml/cic_unification/cicUnification.ml | 535 +++---------------- 1 file changed, 69 insertions(+), 466 deletions(-) diff --git a/helm/ocaml/cic_unification/cicUnification.ml b/helm/ocaml/cic_unification/cicUnification.ml index 164a9cdce..50387922d 100644 --- a/helm/ocaml/cic_unification/cicUnification.ml +++ b/helm/ocaml/cic_unification/cicUnification.ml @@ -23,170 +23,22 @@ * http://cs.unibo.it/helm/. *) -exception UnificationFailed;; -exception Free;; -exception OccurCheck;; -exception RelToHiddenHypothesis;; -exception OpenTerm;; +open Printf -(**** DELIFT ****) +exception AssertFailure of string;; +exception UnificationFailure of string;; -(* the delift function takes in input an ordered list of optional terms *) -(* [t1,...,tn] and a term t, and substitutes every tk = Some (rel(nk)) with *) -(* rel(k). Typically, the list of optional terms is the explicit substitution *) -(* that is applied to a metavariable occurrence and the result of the delift *) -(* function is a term the implicit variable can be substituted with to make *) -(* the term [t] unifiable with the metavariable occurrence. *) -(* In general, the problem is undecidable if we consider equivalence in place *) -(* of alpha convertibility. Our implementation, though, is even weaker than *) -(* alpha convertibility, since it replace the term [tk] if and only if [tk] *) -(* is a Rel (missing all the other cases). Does this matter in practice? *) +let debug_print = prerr_endline -exception NotInTheList;; - -let position n = - let rec aux k = - function - [] -> raise NotInTheList - | (Some (Cic.Rel m))::_ when m=n -> k - | _::tl -> aux (k+1) tl in - aux 1 -;; - -(*CSC: this restriction function is utterly wrong, since it does not check *) -(*CSC: that the variable that is going to be restricted does not occur free *) -(*CSC: in a part of the sequent that is not going to be restricted. *) -(*CSC: In particular, the whole approach is wrong; if restriction can fail *) -(*CSC: (as indeed it is the case), we can not collect all the restrictions *) -(*CSC: and restrict everything at the end ;-( *) -let restrict to_be_restricted = - let rec erase i n = - function - [] -> [] - | _::tl when List.mem (n,i) to_be_restricted -> - None::(erase (i+1) n tl) - | he::tl -> he::(erase (i+1) n tl) in - let rec aux = - function - [] -> [] - | (n,context,t)::tl -> (n,erase 1 n context,t)::(aux tl) in - aux -;; - - -(*CSC: maybe we should rename delift in abstract, as I did in my dissertation *) -let delift context metasenv l t = - let module S = CicSubstitution in - let to_be_restricted = ref [] in - let rec deliftaux k = - let module C = Cic in - function - C.Rel m -> - if m <=k then - C.Rel m (*CSC: che succede se c'e' un Def? Dovrebbe averlo gia' *) - (*CSC: deliftato la regola per il LetIn *) - (*CSC: FALSO! La regola per il LetIn non lo fa *) - else - (match List.nth context (m-k-1) with - Some (_,C.Def (t,_)) -> - (*CSC: Hmmm. This bit of reduction is not in the spirit of *) - (*CSC: first order unification. Does it help or does it harm? *) - deliftaux k (S.lift m t) - | Some (_,C.Decl t) -> - (*CSC: The following check seems to be wrong! *) - (*CSC: B:Set |- ?2 : Set *) - (*CSC: A:Set ; x:?2[A/B] |- ?1[x/A] =?= x *) - (*CSC: Why should I restrict ?2 over B? The instantiation *) - (*CSC: ?1 := A is perfectly reasonable and well-typed. *) - (*CSC: Thus I comment out the following two lines that *) - (*CSC: are the incriminated ones. *) - (*(* It may augment to_be_restricted *) - ignore (deliftaux k (S.lift m t)) ;*) - (*CSC: end of bug commented out *) - C.Rel ((position (m-k) l) + k) - | None -> raise RelToHiddenHypothesis) - | C.Var (uri,exp_named_subst) -> - let exp_named_subst' = - List.map (function (uri,t) -> uri,deliftaux k t) exp_named_subst - in - C.Var (uri,exp_named_subst') - | C.Meta (i, l1) as t -> - let rec deliftl j = - function - [] -> [] - | None::tl -> None::(deliftl (j+1) tl) - | (Some t)::tl -> - let l1' = (deliftl (j+1) tl) in - try - Some (deliftaux k t)::l1' - with - RelToHiddenHypothesis - | NotInTheList -> - to_be_restricted := (i,j)::!to_be_restricted ; None::l1' - in - let l' = deliftl 1 l1 in - C.Meta(i,l') - | C.Sort _ as t -> t - | C.Implicit as t -> t - | C.Cast (te,ty) -> C.Cast (deliftaux k te, deliftaux k ty) - | C.Prod (n,s,t) -> C.Prod (n, deliftaux k s, deliftaux (k+1) t) - | C.Lambda (n,s,t) -> C.Lambda (n, deliftaux k s, deliftaux (k+1) t) - | C.LetIn (n,s,t) -> C.LetIn (n, deliftaux k s, deliftaux (k+1) t) - | C.Appl l -> C.Appl (List.map (deliftaux k) l) - | C.Const (uri,exp_named_subst) -> - let exp_named_subst' = - List.map (function (uri,t) -> uri,deliftaux k t) exp_named_subst - in - C.Const (uri,exp_named_subst') - | C.MutInd (uri,typeno,exp_named_subst) -> - let exp_named_subst' = - List.map (function (uri,t) -> uri,deliftaux k t) exp_named_subst - in - C.MutInd (uri,typeno,exp_named_subst') - | C.MutConstruct (uri,typeno,consno,exp_named_subst) -> - let exp_named_subst' = - List.map (function (uri,t) -> uri,deliftaux k t) exp_named_subst - in - C.MutConstruct (uri,typeno,consno,exp_named_subst') - | C.MutCase (sp,i,outty,t,pl) -> - C.MutCase (sp, i, deliftaux k outty, deliftaux k t, - List.map (deliftaux k) pl) - | C.Fix (i, fl) -> - let len = List.length fl in - let liftedfl = - List.map - (fun (name, i, ty, bo) -> - (name, i, deliftaux k ty, deliftaux (k+len) bo)) - fl - in - C.Fix (i, liftedfl) - | C.CoFix (i, fl) -> - let len = List.length fl in - let liftedfl = - List.map - (fun (name, ty, bo) -> (name, deliftaux k ty, deliftaux (k+len) bo)) - fl - in - C.CoFix (i, liftedfl) - in - let res = - try - deliftaux 0 t - with - NotInTheList -> - (* This is the case where we fail even first order unification. *) - (* The reason is that our delift function is weaker than first *) - (* order (in the sense of alpha-conversion). See comment above *) - (* related to the delift function. *) -prerr_endline "!!!!!!!!!!! First Order UnificationFailed, but maybe it could have been successful even in a first order setting (no conversion, only alpha convertibility)! Please, implement a better delift function !!!!!!!!!!!!!!!!" ; - raise UnificationFailed - in - res, restrict !to_be_restricted metasenv -;; - -(**** END OF DELIFT ****) - -type substitution = (int * Cic.term) list +let type_of_aux' metasenv subst context term = + try + CicMetaSubst.type_of_aux' metasenv subst context term + with CicMetaSubst.MetaSubstFailure msg -> + raise (AssertFailure + ((sprintf + "Type checking error: %s in context\n%s.\nException: %s.\nBroken invariant: unification must be invoked only on well typed terms" + (CicPp.ppterm (CicMetaSubst.apply_subst subst term)) + (CicMetaSubst.ppcontext subst context) msg))) (* NUOVA UNIFICAZIONE *) (* A substitution is a (int * Cic.term) list that associates a @@ -196,7 +48,7 @@ type substitution = (int * Cic.term) list fo_unif_new takes a metasenv, a context, two terms t1 and t2 and gives back a new substitution which is _NOT_ unwinded. It must be unwinded before applying it. *) - + let rec fo_unif_subst subst context metasenv t1 t2 = let module C = Cic in let module R = CicReduction in @@ -217,7 +69,12 @@ let rec fo_unif_subst subst context metasenv t1 t2 = R.are_convertible context t1' t2' ) true ln lm in - if ok then subst,metasenv else raise UnificationFailed + if ok then + subst,metasenv + else + raise (UnificationFailure (sprintf + "Error trying to unify %s with %s: the algorithm only tried to check convertibility of the two substitutions" + (CicPp.ppterm t1) (CicPp.ppterm t2))) | (C.Meta (n,l), C.Meta (m,_)) when n>m -> fo_unif_subst subst context metasenv t2 t1 | (C.Meta (n,l), t) @@ -228,12 +85,12 @@ let rec fo_unif_subst subst context metasenv t1 t2 = let lifted_oldt = S.lift_meta l oldt in fo_unif_subst subst context metasenv lifted_oldt t with Not_found -> - let t',metasenv' = delift context metasenv l t in + let t',metasenv' = CicMetaSubst.delift context metasenv l t in (n, t')::subst, metasenv' in let (_,_,meta_type) = List.find (function (m,_,_) -> m=n) metasenv' in - let tyt = CicTypeChecker.type_of_aux' metasenv' context t in + let tyt = type_of_aux' metasenv' subst' context t in fo_unif_subst subst' context metasenv' (S.lift_meta l meta_type) tyt | (C.Var (uri1,exp_named_subst1),C.Var (uri2,exp_named_subst2)) | (C.Const (uri1,exp_named_subst1),C.Const (uri2,exp_named_subst2)) -> @@ -241,30 +98,27 @@ let rec fo_unif_subst subst context metasenv t1 t2 = fo_unif_subst_exp_named_subst subst context metasenv exp_named_subst1 exp_named_subst2 else - raise UnificationFailed + raise (UnificationFailure (sprintf + "Can't unify %s with %s due to different constants" + (CicPp.ppterm t1) (CicPp.ppterm t1))) | C.MutInd (uri1,i1,exp_named_subst1),C.MutInd (uri2,i2,exp_named_subst2) -> if UriManager.eq uri1 uri2 && i1 = i2 then fo_unif_subst_exp_named_subst subst context metasenv exp_named_subst1 exp_named_subst2 else - raise UnificationFailed + raise (UnificationFailure (sprintf + "Can't unify %s with %s due to different inductive principles" + (CicPp.ppterm t1) (CicPp.ppterm t1))) | C.MutConstruct (uri1,i1,j1,exp_named_subst1), C.MutConstruct (uri2,i2,j2,exp_named_subst2) -> if UriManager.eq uri1 uri2 && i1 = i2 && j1 = j2 then fo_unif_subst_exp_named_subst subst context metasenv exp_named_subst1 exp_named_subst2 else - raise UnificationFailed - | (C.Rel _, _) - | (_, C.Rel _) - | (C.Sort _ ,_) - | (_, C.Sort _) - | (C.Implicit, _) - | (_, C.Implicit) -> - if R.are_convertible context t1 t2 then - subst, metasenv - else - raise UnificationFailed + raise (UnificationFailure (sprintf + "Can't unify %s with %s due to different inductive constructors" + (CicPp.ppterm t1) (CicPp.ppterm t1))) + | (C.Implicit, _) | (_, C.Implicit) -> assert false | (C.Cast (te,ty), t2) -> fo_unif_subst subst context metasenv te t2 | (t1, C.Cast (te,ty)) -> fo_unif_subst subst context metasenv t1 te | (C.Prod (n1,s1,t1), C.Prod (_,s2,t2)) -> @@ -295,16 +149,6 @@ let rec fo_unif_subst subst context metasenv t1 t2 = fo_unif_l subst' metasenv' (l1,l2) in fo_unif_l subst metasenv (lr1, lr2) - | (C.Const _, _) - | (_, C.Const _) - | (C.MutInd _, _) - | (_, C.MutInd _) - | (C.MutConstruct _, _) - | (_, C.MutConstruct _) -> - if R.are_convertible context t1 t2 then - subst, metasenv - else - raise UnificationFailed | (C.MutCase (_,_,outt1,t1,pl1), C.MutCase (_,_,outt2,t2,pl2))-> let subst', metasenv' = fo_unif_subst subst context metasenv outt1 outt2 in @@ -314,19 +158,26 @@ let rec fo_unif_subst subst context metasenv t1 t2 = (function (subst,metasenv) -> fo_unif_subst subst context metasenv ) (subst'',metasenv'') pl1 pl2 - | (C.Fix _, _) - | (_, C.Fix _) - | (C.CoFix _, _) - | (_, C.CoFix _) -> + | (C.Rel _, _) | (_, C.Rel _) + | (C.Sort _ ,_) | (_, C.Sort _) + | (C.Const _, _) | (_, C.Const _) + | (C.MutInd _, _) | (_, C.MutInd _) + | (C.MutConstruct _, _) | (_, C.MutConstruct _) + | (C.Fix _, _) | (_, C.Fix _) + | (C.CoFix _, _) | (_, C.CoFix _) -> if R.are_convertible context t1 t2 then subst, metasenv else - raise UnificationFailed + raise (UnificationFailure (sprintf + "Can't unify %s with %s because they are not convertible" + (CicPp.ppterm t1) (CicPp.ppterm t2))) | (_,_) -> if R.are_convertible context t1 t2 then subst, metasenv else - raise UnificationFailed + raise (UnificationFailure (sprintf + "Can't unify %s with %s because they are not convertible" + (CicPp.ppterm t1) (CicPp.ppterm t2))) and fo_unif_subst_exp_named_subst subst context metasenv exp_named_subst1 exp_named_subst2 @@ -340,278 +191,8 @@ try with e -> let uri = UriManager.uri_of_string "cic:/dummy.var" in -prerr_endline ("@@@: " ^ CicPp.ppterm (Cic.Var (uri,exp_named_subst1)) ^ +debug_print ("@@@: " ^ CicPp.ppterm (Cic.Var (uri,exp_named_subst1)) ^ " <==> " ^ CicPp.ppterm (Cic.Var (uri,exp_named_subst2))) ; raise e -;; - -let unwind metasenv subst unwinded t = - let unwinded = ref unwinded in - let frozen = ref [] in - let rec um_aux metasenv = - let module C = Cic in - let module S = CicSubstitution in - function - C.Rel _ as t -> t,metasenv - | C.Var _ as t -> t,metasenv - | C.Meta (i,l) -> - (try - S.lift_meta l (List.assoc i !unwinded), metasenv - with Not_found -> - if List.mem i !frozen then raise OccurCheck - else - let saved_frozen = !frozen in - frozen := i::!frozen ; - let res = - try - let t = List.assoc i subst in - let t',metasenv' = um_aux metasenv t in - let _,metasenv'' = - let (_,canonical_context,_) = - List.find (function (m,_,_) -> m=i) metasenv - in - delift canonical_context metasenv' l t' - in - unwinded := (i,t')::!unwinded ; - S.lift_meta l t', metasenv' - with - Not_found -> - (* not constrained variable, i.e. free in subst*) - let l',metasenv' = - List.fold_right - (fun t (tl,metasenv) -> - match t with - None -> None::tl,metasenv - | Some t -> - let t',metasenv' = um_aux metasenv t in - (Some t')::tl, metasenv' - ) l ([],metasenv) - in - C.Meta (i,l'), metasenv' - in - frozen := saved_frozen ; - res - ) - | C.Sort _ - | C.Implicit as t -> t,metasenv - | C.Cast (te,ty) -> - let te',metasenv' = um_aux metasenv te in - let ty',metasenv'' = um_aux metasenv' ty in - C.Cast (te',ty'),metasenv'' - | C.Prod (n,s,t) -> - let s',metasenv' = um_aux metasenv s in - let t',metasenv'' = um_aux metasenv' t in - C.Prod (n, s', t'), metasenv'' - | C.Lambda (n,s,t) -> - let s',metasenv' = um_aux metasenv s in - let t',metasenv'' = um_aux metasenv' t in - C.Lambda (n, s', t'), metasenv'' - | C.LetIn (n,s,t) -> - let s',metasenv' = um_aux metasenv s in - let t',metasenv'' = um_aux metasenv' t in - C.LetIn (n, s', t'), metasenv'' - | C.Appl (he::tl) -> - let tl',metasenv' = - List.fold_right - (fun t (tl,metasenv) -> - let t',metasenv' = um_aux metasenv t in - t'::tl, metasenv' - ) tl ([],metasenv) - in - begin - match um_aux metasenv' he with - (C.Appl l, metasenv'') -> C.Appl (l@tl'),metasenv'' - | (he', metasenv'') -> C.Appl (he'::tl'),metasenv'' - end - | C.Appl _ -> assert false - | C.Const (uri,exp_named_subst) -> - let exp_named_subst', metasenv' = - List.fold_right - (fun (uri,t) (tl,metasenv) -> - let t',metasenv' = um_aux metasenv t in - (uri,t')::tl, metasenv' - ) exp_named_subst ([],metasenv) - in - C.Const (uri,exp_named_subst'),metasenv' - | C.MutInd (uri,typeno,exp_named_subst) -> - let exp_named_subst', metasenv' = - List.fold_right - (fun (uri,t) (tl,metasenv) -> - let t',metasenv' = um_aux metasenv t in - (uri,t')::tl, metasenv' - ) exp_named_subst ([],metasenv) - in - C.MutInd (uri,typeno,exp_named_subst'),metasenv' - | C.MutConstruct (uri,typeno,consno,exp_named_subst) -> - let exp_named_subst', metasenv' = - List.fold_right - (fun (uri,t) (tl,metasenv) -> - let t',metasenv' = um_aux metasenv t in - (uri,t')::tl, metasenv' - ) exp_named_subst ([],metasenv) - in - C.MutConstruct (uri,typeno,consno,exp_named_subst'),metasenv' - | C.MutCase (sp,i,outty,t,pl) -> - let outty',metasenv' = um_aux metasenv outty in - let t',metasenv'' = um_aux metasenv' t in - let pl',metasenv''' = - List.fold_right - (fun p (pl,metasenv) -> - let p',metasenv' = um_aux metasenv p in - p'::pl, metasenv' - ) pl ([],metasenv'') - in - C.MutCase (sp, i, outty', t', pl'),metasenv''' - | C.Fix (i, fl) -> - let len = List.length fl in - let liftedfl,metasenv' = - List.fold_right - (fun (name, i, ty, bo) (fl,metasenv) -> - let ty',metasenv' = um_aux metasenv ty in - let bo',metasenv'' = um_aux metasenv' bo in - (name, i, ty', bo')::fl,metasenv'' - ) fl ([],metasenv) - in - C.Fix (i, liftedfl),metasenv' - | C.CoFix (i, fl) -> - let len = List.length fl in - let liftedfl,metasenv' = - List.fold_right - (fun (name, ty, bo) (fl,metasenv) -> - let ty',metasenv' = um_aux metasenv ty in - let bo',metasenv'' = um_aux metasenv' bo in - (name, ty', bo')::fl,metasenv'' - ) fl ([],metasenv) - in - C.CoFix (i, liftedfl),metasenv' - in - let t',metasenv' = um_aux metasenv t in - t',metasenv',!unwinded -;; - -(* apply_subst_reducing subst (Some (mtr,reductions_no)) t *) -(* performs as (apply_subst subst t) until it finds an application of *) -(* (META [meta_to_reduce]) that, once unwinding is performed, creates *) -(* a new beta-redex; in this case up to [reductions_no] consecutive *) -(* beta-reductions are performed. *) -(* Hint: this function is usually called when [reductions_no] *) -(* eta-expansions have been performed and the head of the new *) -(* application has been unified with (META [meta_to_reduce]): *) -(* during the unwinding the eta-expansions are undone. *) - -let apply_subst_reducing subst meta_to_reduce t = - (* andrea: che senso ha questo ref ?? *) - let unwinded = ref subst in - let rec um_aux = - let module C = Cic in - let module S = CicSubstitution in - function - C.Rel _ - | C.Var _ as t -> t - | C.Meta (i,l) as t -> - (try - S.lift_meta l (List.assoc i !unwinded) - with Not_found -> - C.Meta (i,l)) - | C.Sort _ as t -> t - | C.Implicit as t -> t - | C.Cast (te,ty) -> C.Cast (um_aux te, um_aux ty) - | C.Prod (n,s,t) -> C.Prod (n, um_aux s, um_aux t) - | C.Lambda (n,s,t) -> C.Lambda (n, um_aux s, um_aux t) - | C.LetIn (n,s,t) -> C.LetIn (n, um_aux s, um_aux t) - | C.Appl (he::tl) -> - let tl' = List.map um_aux tl in - let t' = - match um_aux he with - C.Appl l -> C.Appl (l@tl') - | _ as he' -> C.Appl (he'::tl') - in - begin - match meta_to_reduce,he with - Some (mtr,reductions_no), C.Meta (m,_) when m = mtr -> - let rec beta_reduce = - function - (n,(C.Appl (C.Lambda (_,_,t)::he'::tl'))) when n > 0 -> - let he'' = CicSubstitution.subst he' t in - if tl' = [] then - he'' - else - beta_reduce (n-1,C.Appl(he''::tl')) - | (_,t) -> t - in - beta_reduce (reductions_no,t') - | _,_ -> t' - end - | C.Appl _ -> assert false - | C.Const (uri,exp_named_subst) -> - let exp_named_subst' = - List.map (function (uri,t) -> (uri,um_aux t)) exp_named_subst - in - C.Const (uri,exp_named_subst') - | C.MutInd (uri,typeno,exp_named_subst) -> - let exp_named_subst' = - List.map (function (uri,t) -> (uri,um_aux t)) exp_named_subst - in - C.MutInd (uri,typeno,exp_named_subst') - | C.MutConstruct (uri,typeno,consno,exp_named_subst) -> - let exp_named_subst' = - List.map (function (uri,t) -> (uri,um_aux t)) exp_named_subst - in - C.MutConstruct (uri,typeno,consno,exp_named_subst') - | C.MutCase (sp,i,outty,t,pl) -> - C.MutCase (sp, i, um_aux outty, um_aux t, - List.map um_aux pl) - | C.Fix (i, fl) -> - let len = List.length fl in - let liftedfl = - List.map - (fun (name, i, ty, bo) -> (name, i, um_aux ty, um_aux bo)) - fl - in - C.Fix (i, liftedfl) - | C.CoFix (i, fl) -> - let len = List.length fl in - let liftedfl = - List.map - (fun (name, ty, bo) -> (name, um_aux ty, um_aux bo)) - fl - in - C.CoFix (i, liftedfl) - in - um_aux t -;; - -(* UNWIND THE MGU INSIDE THE MGU *) -let unwind_subst metasenv subst = - let identity_relocation_list_for_metavariable i = - let (_,canonical_context,_) = - List.find (function (m,_,_) -> m=i) metasenv - in - let canonical_context_length = List.length canonical_context in - let rec aux = - function - n when n > canonical_context_length -> [] - | n -> (Some (Cic.Rel n))::(aux (n+1)) - in - aux 1 - in - List.fold_left - (fun (unwinded,metasenv) (i,_) -> - let identity_relocation_list = - identity_relocation_list_for_metavariable i - in - let (_,metasenv',subst') = - unwind metasenv subst unwinded (Cic.Meta (i,identity_relocation_list)) - in - subst',metasenv' - ) ([],metasenv) subst -;; - -let apply_subst subst t = - (* metasenv will not be used nor modified. So, let's use a dummy empty one *) - let metasenv = [] in - let (t',_,_) = unwind metasenv [] subst t in - t' -;; (* A substitution is a (int * Cic.term) list that associates a *) (* metavariable i with its body. *) @@ -622,5 +203,27 @@ let apply_subst subst t = (* metavariables may have been restricted. *) let fo_unif metasenv context t1 t2 = let subst_to_unwind,metasenv' = fo_unif_subst [] context metasenv t1 t2 in - unwind_subst metasenv' subst_to_unwind + CicMetaSubst.unwind_subst metasenv' subst_to_unwind ;; + +let fo_unif_subst subst context metasenv t1 t2 = + let enrich_msg msg = + sprintf "Unification error unifying %s of type %s with %s of type %s in context\n%s\nand metasenv\n%s\nbecause %s" + (CicPp.ppterm (CicMetaSubst.apply_subst subst t1)) + (try + CicPp.ppterm (type_of_aux' metasenv subst context t1) + with _ -> "MALFORMED") + (CicPp.ppterm (CicMetaSubst.apply_subst subst t2)) + (try + CicPp.ppterm (type_of_aux' metasenv subst context t2) + with _ -> "MALFORMED") + (CicMetaSubst.ppcontext subst context) + (CicMetaSubst.ppmetasenv subst metasenv) msg + in + try + fo_unif_subst subst context metasenv t1 t2 + with + | AssertFailure msg -> raise (AssertFailure (enrich_msg msg)) + | UnificationFailure msg -> raise (UnificationFailure (enrich_msg msg)) +;; + -- 2.39.2