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|ID||Project||Category||View Status||Date Submitted||Last Update|
|0007519||OCaml||typing||public||2017-04-20 20:44||2017-08-02 07:55|
|Target Version||Fixed in Version|
|Summary||0007519: Incorrect rejection of program due to faux scope escape|
|Description||The following program is rejected by the compiler:|
module Gen_spec = struct type 't extra = unit end
module type S = sig
module Spec : sig type 't extra = unit end
val make : unit -> t Spec.extra
end (* S *)
module Make () : S with module Spec := Gen_spec = struct
type t = int
let make () = ()
end (* Make *)
let () =
let module M = Make () in
(* (M.make () : unit) *)
The error is:
File "./foo.ml", line 17, characters 2-11:
Error: This expression has type M.t Gen_spec.extra = unit
but an expression was expected of type unit
The type constructor M.t would escape its scope
The error shows that the compiler already knows that M.t Gen_spec.extra is equivalent to the unit type. Therefore, there should not be any type escaping the scope of the local module. Using the commented out last line instead of the preceding one also shows that the compiler will happily unify the type with "unit" and then accept the program.
I suppose that there is a missing conversion somewhere in the type checker that should attempt to eliminate all local types before complaining about scope violations.
|Tags||No tags attached.|
The interesting phenomenon here is that one needs to expand extra, not t, to avoid the escape.
This is nowhere in the logic of the compiler at this point.
This can be done, but the runtime cost could be significant (should check).
|Tentative fix: https://github.com/ocaml/ocaml/pull/1273 [^]|
|2017-04-20 20:44||mottl||New Issue|
|2017-08-02 06:58||garrigue||Note Added: 0018155|
|2017-08-02 06:58||garrigue||Assigned To||=> garrigue|
|2017-08-02 06:58||garrigue||Status||new => confirmed|
|2017-08-02 07:55||garrigue||Note Added: 0018156|
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