On Tue, Aug 12, 2008 at 8:02 PM, Andreas Raab <andreas.raab at gmx.de> wrote:
>
> I think we'll have to agree that the result is undefined if the collection
> contains elements that can't be summed up. While one can rewrite the method
> to deal with the specific problem you are describing like here:
>
> Collection>>sum
>   "Answer the sum of elements, or nil if empty"
>   | first sum |
>   first := true.
>   self do:[:each|
>     first
>       ifTrue:[sum := each. first := false]
>       ifFalse:[sum := sum + each]].
>  ^sum
>
> such that
>
>  {nil. 3} sum. => Error
>  {3. nil} sum. => Error
>
> it just seems to me that the result of, e.g.,
>
>  #() sum => nil
>  {nil} sum => nil
>
> is just as bad. I think that every proposed implementation has problems
> similar to these and I don't think it's addressable without unreasonable
> burden on both elements as well as implementation.
>
> Cheers,
>  - Andreas

>From my side, I just see #sum as convenience math utility (like
#average which is also in there).  I just wanted to see #reduce
included so this "add a sample then take it out again" could go away.
Purely for a teaching point of view, that is, I would rather new
programmers learn to refactor and build the language to their needs
instead of making strange work arounds to deal with "close but not
quite right" methods.