[plt-scheme] undefined value

If Scheme's type analysis ever matures enough,

   (define-struct mtdb ())

will be your best bet. You get a unique value (make-mtdb) and a 
matching predicate mtdb?.

-- Matthias



On Oct 30, 2004, at 12:33 PM, David J. Neu wrote:

>   For list-related administrative tasks:
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>
> Hi all,
>
> Which would be the appropriate PLT Scheme value to use to represent a
> NULL value in a database?
>
> For example, in Python I'd use None, in C NULL, in Pascal nil.
>
> The value will be part of an association list that represents a row in
> a database, i.e. ((field1 . value1) (field2 . value2) ...) and will be
> returned from a mzscheme extension.
>
> I've been using 'null but that seems wrong.
>
> I've been considering scheme_void or scheme_undefined.
>
> I'd obviously want to be able to use an existing procedure or write
> new one to checks if the value of a field is NULL.
>
> Many thanks!
>
> Cheers,
> Dave