my @evens = @all[map $_*2+1, 0..$#all/2];
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my @evens = @all[grep !($_ % 2), 0..$#all];    # even-index elements
my @odds  = @all[grep $_ % 2, 0..$#all];       # odd-index  elements
[download]

(update: fixed off-by-one error, in case of uneven number of elements)