Calculations for spanner before its print function is called

[Mike Solomon]

Hey lilypond developers,
    I am toying around with a new spanner, and before it prints, I need to
do some calculations on all of its broken_intos_.  I can easily do these
calculations in the print function by accessing the broken_into_ of
spanner->original (), but then this calculation is done for each time print
is called, which is N-1 times too many (where N is the length of
broken_into_).  The code works just fine, but it is overkill: is there a way
to perform operations on a spanner and its broken_into_'s once before the
print function is called?

Thanks!
~Mike