programmatic pure-print stumbling block

[Mike Solomon]

Hey all,
    I recently tried to programmatically add a pure-print function to the
list of pure-print functions using the setter method I proposed, which sent
lilypond into a 13+h spiral of compilation in functions having to do with
skylines and page breaks that I don't really understand (this is what gdp
tells me).  In order to create a print function that works as a pure-print
function, is there a series of steps one has to go through:

(a) to design the function (is there anything that a pure-print callback
neeeeds to do or not do, both in terms of its return value and internal
operation)?
(b) to register the function in various places (what parts of lilypond aside
from the list pure-print-callbacks in scm/define-grobs.scm need to know
about these functions)?

Thanks!
~Mike