Can someone clarify what this Joel On Software quote means?
- by Bob
I was reading Joel On Software today and ran across this quote:
Without understanding functional
programming, you can't invent
MapReduce, the algorithm that makes
Google so massively scalable. The
terms Map and Reduce come from Lisp
and functional programming. MapReduce
is, in retrospect, obvious to anyone
who remembers from their
6.001-equivalent programming class that purely functional programs have
no side effects and are thus trivially
parallelizable.
What does he mean when he says functional programs have no side effects? And how does this make parallelizing trivial?