[ebon-discuss] Possible grammar error in indirections in client relations.

[Joseph R. K. <ki...@ac...>]

The BON grammar specifies indirections in client relations with the =
following rules:

      Client_relation =3D          Client client [ Client_entities ]
                                 [ Type_mark ] Supplier [ Semantic_label ]
      Client_entities =3D          "{" Client_entity_expression "}"
      Client_entity_expression =3D Client_entity_list | Multiplicity
      Client_entity_list =3D       { Client_entity "," ...} +
      Client_entity =3D            Feature_name | Supplier_indirection |
                                 Parent_indirection
      Supplier_indirection =3D     [ Indirection_feature_part ":" ]
                                 Generic_indirection
      Indirection_feature_part =3D Feature_name | Indirection_feature_list
      Indirection_feature_list =3D "(" Feature_name_list ")"
      Parent_indirection =3D       "->" Generic_indirection

      Generic_indirection =3D Formal_generic_name | Named_indirection
      Named_indirection =3D   Class_name "[" Indirection_list "]"
      Indirection_list =3D    { Indirection_element "," ...} +
      Indirection_element =3D "..." | Named_indirection
      Type_mark =3D           ":" | ":{" | Shared_mark
      Shared_mark =3D         ":" "(" Multiplicity ")"

But the textual examples from the Wald=E9n/Nerson text seemingly violate =
this =
grammar (from Figure B.8, pg. 371):

        NURSE client {patients: LIST[..., PATIENT_ID]} PATIENT

Note that PATIENT_ID is a Class_name without any parameterized =
Indirection_list.  I suggest that the grammar is erroneous, not the =
examples.  At first blush, I take the meaning of the specification of the =
classname in the parameter as a generic type-narrowing, kind of a type =
currying.  Of course, this leaves open the possible semantics for the =
ellipses ("...") construct...

I haven't yet re-read the appropriate parts of the text to understand the =
intent of such constructs.  Therefore, I'm not going to suggest a revised =
grammar at this time.

If anyone has input on this I'd appreciate hearing it.

Note that, since we are extended the language anyway, if the extended BON =
grammar covers (algebraically) the existing (possibly corrected) BON =
grammar and doesn't violate the latter's semantics, then we can add =
constructs like the above type currying if we choose.

Joe
--
Joseph R. Kiniry                    http://www.cs.caltech.edu/~kiniry/
California Institute of Technology        ID 78860581      ICQ 4344804