[MLton] Re: [Smlnj-dev-list] SML/NJ (possible) bug report

[David MacQueen]

Thanks for the bug report.   Pragmatically it certainly seems like a 
bug, and
this should be made clear in some supplementary documentation (where
as opposed to where type is, unfortunately, not in the SML 97 
definition).

Dave

On Jan 2, 2004, at 6:03 PM, Matthew Fluet wrote:

>
> Number: *
> Title:       compiler bug reported on inconsistent signature
> Keywords:    where, where type, signature
> Submitter:   Matthew Fluet (fluet@cs.cornell.edu)
> Date:        01/02/04
> Version:     110.44
> System:	     x86-linux
> Severity:    minor/cosmetic
> Problem:
>
> A combination of where and where type clauses can give rise to a 
> signature
> with inconsistent constraints.  The inconsistency is not reported (as a
> type error) at the time of the signature definition.  Attempting to 
> match
> a structure against such a signature gives a type error (correct, as no
> structure can satisfy both of the constraints), but also gives an 
> "Error:
> Compiler bug:" message.
>
> I'm not sure whether the failure to give an earlier type error is a 
> bug;
> it depends upon the exact semantics of a where clause (which I can't 
> find
> documented on the SML/NJ site).  The "Error: Compiler bug:"
> message suggests a unanticipated corner case.
>
> Code:
>
> signature T = sig type t end;
> structure R = struct type t = int end;
> signature T = sig type t end;
> structure R = struct type t = int end;
> structure S = struct type t = bool end;
> signature SIG =
>   sig
>     structure T : T where type t = R.t
>   end
>   where T = S;
>
> structure A : SIG =
>   struct structure T = R end;
> structure B : SIG =
>   struct structure T = S end;
>
> Transcript:
>
> Standard ML of New Jersey v110.44 [FLINT v1.5], November 6, 2003
> - signature T = sig type t end;
> signature T = sig type t end
> - structure R = struct type t = int end;
> structure R : sig type t = int end
> - structure S = struct type t = bool end;
> structure S : sig type t = bool end
> - signature SIG =
> = sig structure T : T where type t = R.t
> = end where T = S;
> signature SIG = sig structure T : sig type t = t end end
> - structure A : SIG =
> = struct structure T = R end;
> stdIn:7.1-8.27 Error: structure def spec for T not matched
> - structure B : SIG =
> = struct structure T = S end;
> stdIn:1.1-9.27 Error: type t does not match definitional specification
> Error: Compiler bug: ModuleUtil: unexpected binding in extractInfo
>
> Comments:
>
> The same behavior appears if SIG uses a definitional type 
> specification:
>
> signature SIG2 =
>   sig
>     structure T : sig type t = R.t end
>   end
>   where T = S
>
> On the other hand, there are appropriate type-error messages for:
>
> signature SIG3 =
>   sig
>     structure T : T where type t = R.
>   end
>   where type T.t = S.t
>
> It is my understanding that SIG and SIG3 are supposed to be equivalent.
>
> Fix:	     <optional - but you get extra credit>
> Test: *
> Owner: *
> Status: *
>
>
>
>
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