(**** DELIFT ****)
-(* the delift function takes in input an ordered list of integers [n1,...,nk]
- and a term t, and relocates rel(nk) to k. Typically, the list of integers
- is a parameter of a metavariable occurrence. *)
+(* 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? *)
exception NotInTheList;;
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
;;
+(*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
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,_)) -> deliftaux k (S.lift m t)
+ 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) ->
- (* It may augment to_be_restricted *)
- ignore (deliftaux k (S.lift m 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) ->
in
C.CoFix (i, liftedfl)
in
- let res = deliftaux 0 t 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
;;
(* 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