[GRASS5] variables in mapcalc, reusability

[cgnicholas at alamedanet.net]

greetings - 

I am (finally) getting a chance to play with mapcalc in order to
examine  "hot spots" in mosaics of aerial imagery. 

I was thinking to make a mapcalc routine similar to r.slope.aspect to
determine angle of incidence from the camera position to anywhere on a
DEM, so I can play with various BDRF functions and the outputs from
r.sun.

But I'm wondering: is there an elegant way to pass global parameters
(like x,y,z, input DEM, output files, etc) into a *reusable* chunk of
mapcalc, that I can script for a lot of photos? Or do I need to invent
some kind of (m4-based?) preprocessor that spits out a fresh piece of
mapcalc for each frame? 

I can imagine such a preprocessor doing simple things like #include,
$1, $2, etc variable substitutions, etc. (Indeed, might such a
preprocessor be able to eventually take a graph of model descriptions
in something like MML, as per:
http://www.uvm.edu/giee/SME3/MetaModelsF.html and spit out mapcalc and
a controlling shell script to exercise it....?)

Or is this completely the wrong way to approach this kind of problem? 

thanks in advance - 

Chris Nicholas