Absolute/relative scale conversions

[J. David Blackstone]

  In my attempt to write a shaped-note music feature for lilypond, I 
need to convert absolute pitches (as in C, D, E, F#, etc.) to
relative/solfege pitches (Do, Re, Mi, Fi, etc.).  I started working on
a class for this, but I thought it'd be smart to check before
reinventing the wheel.

  Does code to do this exist anywhere in Lilypond already?  I don't
need to actually get to solfege syllable names (as in "do"); I just
need to get the intervals from the key tone.  (i.e., numbers would
suffice, such as 0, 1, 2, 3.5 or perhaps some other convention).

  Thanks in advance for any info provided.

J. David Blackstone