[Proj] Projection Dev - How to call other projections from a projection?

[Michael Speth]

Greetings,
   I am working on implementing a new projection and stumped on how to 
call a projection from within a projection.

For example, the projection has both a spheroid and ellipsoid.  The 
function for determine the projection of the ellipsoid (both forward and 
inverse) use their respective spheroid projections during calculation.  
Unfortunately, I'm not sure if the ENTRY function can be used because 
for the ellipsoid calculation, but the spheroid function is only an 
intermediate step int the calculation and there exists additional 
computations after the spheroid function is called.

Consider this example:

INVERSE(e_inverse);
    lp = INVERSE(p_inverse);
    lp.phi = auth_lat(...);
    return lp;

Does this make sense?  If so, is there any way of calling the inverse 
function for sphere within the inverse function for ellipsoid?

Thank you for your help
Michael Speth
Landcare Research
Scientific Programmer