Lazy, parallel multiple value reductions in Common Lisp

Reductions, folds, or catamorphisms are an important component of every
functional programmer's toolbox.  However, common manifestations of these
operators can only operate on a single sequence at once and don't have
any potential for parallel execution.

We present a new, parallelizable reduction operator that can
simultaneously reduce $k$ arrays at once, using a function with $2k$
arguments and $k$ return values.  We then discuss an efficient
implementation of this new reduction operator as part of the Petalisp
project.