Re: void as a return value (Re: [Chicken-users] DBI)

[Ozzi]

Vincent Manis wrote:
> \begin{rant}
> On the subject of using void as a return value (rather than to indicate 
> that
> a function or method doesn't return anything), EWWWW.
>
> Please, please, don't ever write functions that return void as anything 
> other
> than an indication that no value was returned.
>
> #;44> (car (db-fetch-row (db-query "select salary where empname='Bilbo 
> Baggins'")))
> #;45>

I don't yet have an opinion on using void, but this function would return either

a list: ( (void) )
or an alist: ( (salary . (void) )

depending on which we used to represent rows. Either way, there would indeed be 
a return value.

> So now, (a) you get no output, which might be mystifying and (b) car is 
> now returning
> void. Neither of these violates any language rule, but each violates the 
> Law of
> Least Astonishment.
>
> For SQL nulls, one could use '(), as has been mentioned; alternatively, 
> an object
> called the-SQL-null-object could be created (perhaps as a record type 
> value).
>
> Incidentally, there are several different meanings for null in SQL, 
> including no
> information, not applicable, no value presently exists (but one might in 
> the future),
> etc. You can find lengthy essays on the appropriateness of using NULL in 
> several
> of Chris Date's `Writings on Database' books. People have enough trouble 
> understanding
> SQL null without further conflating it with `this function returns no 
> values'.
>
> \end{rant}
>
> Sorry :-) -- vincent
>
>
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