>How can I pass an array as a parameter to a function and then get a different array back as the results of that function???

You'll have to pass two arrays (both by reference), one input and another output.

DIMENSION laIn[1], laOut[1]
= ADIR(laIn, "*.*")
lnResult = MyArrayFunc(@laIn, @laOut)
...
FUNCTION MyArrayFunc(taIn, taOut)

...