Re: Another spurious compilation diagnostic?

Thank you for your assistance.

It looks like you are correct.  However, while the compiler may be  
smart, it's not smart enough to see that there's a secondary guard  
variable that prevents any access of the list-length result if the  
argument is nil.  The same goes for the when evaluation.

== Steven


On Sep 23, 2008, at 2:12 AM, Madhu wrote:

> 	[pardon the top post, if you find it inappropriate]
>
> The CLHS entry for LIST-LENGTH says:
>
> ,----
> | Returns the length of list if list is a proper list. Returns nil if
> | list is a circular list.
> `----
>
> This means one of the possible return values is NIL.  The compiler
> diagnostics seem to indicate that it has inferred that the value
> returned by LIST-LENGTH are used only in number contexts.
>
> The compiler is warning you that there will be an error in the event
> LIST-LENGTH returns NIL.
>
> I suspect the case with the other diagnostic is similar. It is likely
> you are using the return value of a (WHEN clause) where the compiler
> always expects a number.
>
> Both of these deal with the specifics of your code , so it is likely
> the compiler knows better (as it has access to the code) than us (who
> dont:)