running pure functions in parallel

[Justin]

I'm designing an application which needs to process a lot of data as quickly as
possible. I've found that I can engineer the processing algorithms into pure
functions which can operate on different segments of my data. I would like to
run these functions in parallel but:

spawn() precludes returning a value
the docs seem to be silent on the possibility of using out parameters

Do I have to use messaging passing to get a value out of a pure function being
run in a separate thread?