Re: argument against using '() for null values? ([Chicken-users] DBI)

[Ozzi]

> Three that I can think of:
>
> 1) It would make alist representations ugly:
> (query "select foo, NULL as bar, baz from stuff") =>
> ((foo . 1) (bar) (baz . "a string"))

This doesn't bother me.

> 2) It is not a disjoint type. (list? '()) => #t. That's bad.
>
> 3) As a special case of (2), some databases have array-type columns.
> An empty list may be a valid column value.

All right, there's the big problem.

How about keeping '() for sql NULL, and using vectors to represent array-type 
columns?

Since SQL NULL values are common, I really like the simple null? test. It's 
intuitive.

On the other hand, I didn't even know array-type columns existed until tonight. 
I'd prefer to go with something slightly less intuitive for representing them if 
it will let us use '() for NULL.

Thoughts?

> Personally, I'm okay with (void), though Vincent's comment about
> displaying results is a good one. I think the only logical alternative
> to (void) is a #<sql-null> value, similar in implementation to
> #<undefined>: a disjoint type plus a predicate. (Currently that's how
> the postgresql egg handles it.)
>
> Graham