Re: [bug-recutils] Field predefined types

[Jose E. Marchesi]

Hi JF.
    
    I would like to expose an idea of mine; Its objective is to help
    lazy people as I to write repetitive descriptors.  We already have
    predefined field types, like "date" and "email", I suggest to allow
    the declaration of user-predefined types.

That is a very good idea, to support named user-defined types.  However,
your prososed %define directive would invalidate one of the premises of
the format: rec data is a sequence of record sets, and record sets are
sequences of records.  It follows that the only contents allowed in a
rec file are comments and records.  The line:

    %define FullName regexp /^[A-Z][a-zA-Z-]+ [A-Z][a-zA-Z-]+$/

is neither a comment or a record.  Even if we turn it into a field, and
place the field before the other record sets:

/
| %define: FullName int
|
| %rec: foo
| ...
|
| %rec: bar
|
| ...
\

The record containing %define would pertain to the "default" unnamed
record set, since it is not a record descriptor: it is lacking the %rec:
field.

I have a suggestion for a different implementation of the same
principle, that would fit better in the recfiles design.  This solution
is based in two additions to the format:

1) A %typedef special field, that can be used to define named user
   defined types.  As with any other special field, it shall appear in a
   record descriptor and will have effect in the records contained in
   the record set.  The synopsis is:

   %typedef: TYPE_NAME TYPE_DESCRIPTION

   where TYPE_NAME is the name of the type.  It shall follow the same
   rules than field name parts.  The type name can be used in any place
   where a type description is expected.

   For example:

   %rec: Person
   %typedef: IdNumber regexp /[0-9]{5}[a-zA-Z]/
   %type: Id    IdNumber
   %type: OldId IdNumber

   Note how both Id and OldId are defined using the same user defined
   type 'IdNumber'.

   Since a type name can appear anywhere a type description is required,
   it is possible to "chain" typedefs:

   %typedef: BasicCode regexp /../
   %typedef: PersonId BasicCode
   %typedef: GroupId  BasicCode

2) The ability of referring to types defined in other record sets.  We
   could do it by allowing the usage of type names like:

   RECORD_TYPE:TYPE_NAME

   For example:

   %rec: Person
   %typedef: PersonId regexp /.../
   %type: Id PersonId
   ...
 
   %rec: Group
   %type: Id Person:PersonId

   Note that it would not be allowed to such compound type names in
   %typedef.

What do you think?

-- 
Jose E. Marchesi    address@hidden
GNU Project         http://www.gnu.org