On Sun, Mar 30, 2008 at 08:21:39AM -0700, Mark A. Biggar wrote:
> The reduce meta-operator over - in APL gives alternating sum, similarly
> alternating quotient for /, which only works if you right associate
> things.
>
> [-] 1,2,3,4,5,6 => 1-2+3-4+5-6 # pseudo-apl
>
> [/] 1,2,3,4,5,6 => (1*3*5)/(2*4*6) #pseudo-apl
>
> note that would break the perl 6 simple rule that [-] 1,2,3 => 1-2-3,
> but gives something much more useful. There currently is no easy way to
> do alternating sum/quotient in perl6.
How about...?
# alternating sum of elements in @list
$altsum = [+] ({ $^a - $^b } for @list);
Pm
