The error you are writing about is right here:

>> ;;;; function definition
>> (define (eps-func p)

>>    (let* ((p (lattice->cartesian)) <------

>>              (x (vector3-x p))
>>              (y (vector3-y p))
>>              (z (vector3-z p)))
>> (if (> sin(* 2 pi x y z) 0)
>>                 (make dielectric
>>                         (epsilon 12))
>>                 (make dielectric
>>                         (epsilon 1)))))

You call the function lattice->cartesian there with no arguments, but
it expects one argument.

Noah

> Regards,
>
> Simon